Ketoreductase polypeptides for the production of azetidinone

ABSTRACT

The present disclosure provides engineered ketoreductase enzymes having improved properties as compared to a naturally occurring wild-type ketoreductase enzyme. Also provided are polynucleotides encoding the engineered ketoreductase enzymes, host cells capable of expressing the engineered ketoreductase enzymes, and methods of using the engineered ketoreductase enzymes to synthesize a variety of chiral compounds.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. application Ser.No. 16/790,474, filed Feb. 13, 2020, which is a Divisional of U.S.application Ser. No. 16/404,988, filed May 7, 2019, now U.S. Pat. No.10,597,641, which is a Divisional of U.S. application Ser. No.15/631,359, filed Jun. 23, 2017, now U.S. Pat. No. 10,329,540, which isa Continuation of U.S. application Ser. No. 15/408,673, filed Jan. 18,2017, now U.S. Pat. No. 9,719,071, which is a Continuation of U.S.application Ser. No. 15/272,664, filed Sep. 22, 2016, now U.S. Pat. No.9,580,694, which is a Divisional of U.S. application Ser. No.15/175,317, filed Jun. 7, 2016, now U.S. Pat. No. 9,476,034, whichclaims benefit under 35 U.S.C. § 120 of U.S. application Ser. No.14/822,624, filed Aug. 10, 2015, now U.S. Pat. No. 9,382,519, whichclaims benefit under 35 U.S.C. § 120 of U.S. application Ser. No.14/658,407, filed Mar. 16, 2015, now U.S. Pat. No. 9,133,442, whichclaims benefit under 35 U.S.C. § 120 of U.S. application Ser. No.13/925,096, filed Jun. 24, 2013, now U.S. Pat. No. 8,980,606, whichclaims benefit under 35 U.S.C. § 120 of U.S. application Ser. No.13/569,900, filed Aug. 8, 2012, now U.S. Pat. No. 8,470,572, which is aDivisional of U.S. application Ser. No. 12/977,825, filed Dec. 23, 2010,now U.S. Pat. No. 8,257,952, which is a Continuation of U.S. applicationSer. No. 12/243,968, filed Oct. 1, 2008, now U.S. Pat. No. 7,883,879,and under 35 U.S.C. § 119(e) of application Ser. No. 60/976,555, filedOct. 1, 2007, the contents of each of which are incorporated herein byreference.

REFERENCE TO SEQUENCE LISTING, TABLE OR COMPUTER PROGRAM

The Sequence Listing concurrently submitted herewith under 37 C.F.R.1.821 in a computer readable form (CRF) via EFS-Web as file name376247-022.txt is herein incorporated by reference in its entirety. Theelectronic copy of the Sequence Listing was created on Oct. 1, 2008,with a file size of 150 Kbytes.

BACKGROUND

Enzymes belonging to the ketoreductase (KRED) or carbonyl reductaseclass (EC1.1.1.184) are useful for the synthesis of optically activealcohols from the corresponding prostereoisomeric ketone substrate orcorresponding racemic aldehyde substrates. KREDs typically convertketones and aldehyde substrate to the corresponding alcohol product, butmay also catalyze the reverse reaction, oxidation of an alcoholsubstrate to the corresponding ketone/aldehyde product. The reduction ofketones and aldehydes and the oxidation of alcohols by enzymes such asKRED requires a co-factor, most commonly reduced nicotinamide adeninedinucleotide (NADH) or reduced nicotinamide adenine dinucleotidephosphate (NADPH), and nicotinamide adenine dinucleotide (NAD) ornicotinamide adenine dinucleotide phosphate (NADP) for the oxidationreaction. NADH and NADPH serve as electron donors, while NAD and NADPserve as electron acceptors. It is frequently observed thatketoreductases and alcohol dehydrogenases accept either thephosphorylated or the non-phosphorylated co-factor (in its oxidized andreduced state).

KRED enzymes can be found in a wide range of bacteria and yeasts (forreviews: Kraus and Waldman, Enzyme catalysis in organic synthesis Vols.1&2.VCH Weinheim 1995; Faber, K., Biotransformations in organicchemistry, 4th Ed. Springer, Berlin Heidelberg New York. 2000; Hummeland Kula, 1989, Eur. J. Biochem. 184:1-13). Several KRED gene and enzymesequences have been reported, e.g., Candida magnoliae (Genbank Acc. No.JC7338; GI:11360538) Candida parapsilosis (Genbank Acc. No. BAA24528.1;GI:2815409), Sporobolomyces salmonicolor (Genbank Acc. No. AF160799;GI:6539734).

In order to circumvent many chemical synthetic procedures for theproduction of key compounds, ketoreductases are being increasinglyemployed for the enzymatic conversion of different keto and aldehydesubstrates to chiral alcohol products. These applications can employwhole cells expressing the ketoreductase for biocatalytic ketonereductions, or purified enzymes in those instances where presence ofmultiple ketoreductases in whole cells would adversely affect thestereopurity and yield of the desired product. For in vitroapplications, a co-factor (NADH or NADPH) regenerating enzyme such asglucose dehydrogenase (GDH), formate dehydrogenase etc. is used inconjunction with the ketoreductase. Examples using ketoreductases togenerate useful chemical compounds include asymmetric reduction of4-chloroacetoacetate esters (Zhou, J. Am. Chem. Soc. 1983 105:5925-5926;Santaniello, J. Chem. Res. (S) 1984:132-133; U.S. Pat. Nos. 5,559,030;5,700,670 and 5,891,685), reduction of dioxocarboxylic acids (e.g., U.S.Pat. No. 6,399,339), reduction of tert-butyl (S)chloro-5-hydroxy-3-oxohexanoate (e.g., U.S. Pat. No. 6,645,746 and WO01/40450), reduction pyrrolotriazine-based compounds (e.g., USapplication No. 2006/0286646); reduction of substituted acetophenones(e.g., U.S. Pat. No. 6,800,477); and reduction of ketothiolanes (WO2005/054491).

It is desirable to identify other ketoreductase enzymes that can be usedto carryout conversion of various keto substrates to its correspondingchiral alcohol products.

SUMMARY

The present disclosure provides ketoreductase polypeptides having theability to reduce a racemic mixture ofmethyl-2-benzamidomethyl-3-oxobutyrate (“the substrate”) to2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate (“the product”),polynucleotides encoding such polypeptides, and methods for using thepolypeptides. The compound2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate is an intermediate inthe synthesis of (2R,3R)-3-((R)-1-(tert-butyldimethylsilyloxy)ethyl)-4-oxoazetidin-2-yl acetate (“azetidinone; acetyoxyazetidinone”;CAS registry 76855-69-1), which is an intermediate (penultimateintermediate) used in the manufacture of various carbapenem antibiotics.Carbapenem antibiotics that can be synthesized from2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate include, but are notlimited to, imipenem, meropenem, doripenem, ertapenem, biopenem,panipenem, and other compounds similar to thienamycin. The engineeredketoreductase polypeptides of the present disclosure have an improvedproperty in reducing or converting the specified substrate to thecorresponding chiral alcohol product as compared to thenaturally-occurring wild-type ketoreductase enzymes obtained fromLactobacillus kefir (“L. kefir”; SEQ ID NO:4), Lactobacillus brevis (“L.brevis”; SEQ ID NO:2), or Lactobacillus minor (“L. minor”; SEQ IDNO:86). In some embodiments, the engineered ketoreductase polypeptideshave an improved property as compared to another engineeredketoreductase polypeptide, such as SEQ ID NO: 48.

In some embodiments, the ketoreductase polypeptides have, with respectto the wild-type L. kefir, L. brevis, or L. minor KRED sequences of SEQID NO:4, 2, and 86, at least the following feature: residue 202 isvaline or leucine. In some embodiments, the ketoreductases of thedisclosure have, with respect to the sequences of SEQ ID NO:4, 2, or 86,at least two of the following features: (1) residue corresponding toposition 94 (i.e., X94) is an aliphatic or polar residue, (2) residuecorresponding to position 199 (i.e., X199) is an aliphatic, polar orconstrained residue, and (3) residue corresponding to position 202(i.e., X202) is valine or leucine. In some embodiments, the polypeptideshave, with respect to the sequences of SEQ ID NO:4, 2, and 86, at leastthe following features: (1) residue corresponding to position X94 is apolar residue, (2) residue corresponding to X199 is an aliphatic,constrained, or polar residue, and (1) residue corresponding to X202 isvaline or leucine.

In addition to the features described above, the ketoreductases can haveone or more residue differences at other residue positions as comparedto the sequences of SEQ ID NO:2, 4, or 86. In some embodiments, theketoreductase polypeptides herein comprise an amino acid sequence thatis at least about 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%,96%, 97%, 98%, 99% or more identical to a reference sequence based onSEQ ID NO: 2, 4 or 86 having the following features: residuecorresponding to X94 is an aliphatic or polar residue, particularlyalanine or threonine; residue corresponding to X199 is an aliphatic,constrained or polar residue, particularly alanine, histidine, orasparagine; and residue corresponding to X202 is valine or leucine; withthe proviso with the proviso that the ketoreductase amino acid sequencehas at least the preceding features, i.e., residue corresponding to X94is an aliphatic or polar residue; residue corresponding to X199 is analiphatic, constrained or polar residue; and residue corresponding toX202 is valine or leucine.

In some embodiments, such as where the improved property is from asingle residue difference or a specific combination of residuedifferences, the engineered ketoreductases may optionally include one ormore residue differences at other positions in the polypeptide ascompared to the reference sequence. In some embodiments, the residuedifference comprise conservative mutations. In some embodiments, theadditional residue differences at other residue positions can beincorporated to produce further improvements in enzyme properties. Theseimprovements can be further increases in enzymatic activity for thedefined substrate, but can also include increases in stereoselectivity,thermostability, solvent stability, and/or reduced product inhibition.Various residue differences that can result in one or more improvedenzyme properties are provided in the detailed description. In someembodiments, an improved ketoreductase polypeptide comprises an aminoacid sequence that corresponds to the sequence formulas as laid out inSEQ ID NO:83, SEQ ID NO:84, or SEQ ID NO:87 (or a region thereof, suchas residues 90-211). SEQ ID NO:84 is based on the wild-type amino acidsequence of the Lactobacillus kefir ketoreductase (SEQ ID NO:4), SEQ IDNO:83 is based on the wild-type amino acid sequence of the Lactobacillusbrevis ketoreductase (SEQ ID NO:2); and SEQ ID NO:87 is based on thewild-type amino acid sequence of the Lactobacillus minor ketoreductase(SEQ ID NO:86). The sequence formulas of SEQ ID NOs:83, 84, and 87specify that residue corresponding to X94 is an aliphatic or polarresidue; residue corresponding to X199 is an aliphatic, constrained orpolar residue; and residue corresponding to X202 is valine or leucine.The sequence formulas further specify features at other residuepositions, as provided in the detailed description.

In some embodiments, the engineered ketoreductase polypeptide can haveincreased enzymatic activity as compared to the wild-type ketoreductaseenzyme for reducing the substrate to the product. Improvements inenzymatic activity can be measured by comparing the specific activity ofthe ketoreductase polypeptide with that of the wild-type ketoreductaseenzyme using standard enzyme assays. The amount of the improvement canrange from 1.5 times (or fold) the enzymatic activity of thecorresponding wild-type or reference ketoreductase enzyme, to as much as2 times, 5 times, 10 times, 20 times, 25 times, 50 times, 75 times, 100times, or more. In specific embodiments, the engineered ketoreductaseenzyme exhibits improved enzymatic activity that is at least 1.5-fold,2-fold, 3-fold, 4-fold, 5-fold, 10-fold, 25-fold, 50-fold, 100-fold,500-fold, or 1000-fold greater than that of the wild-type or referenceketoreductase enzyme. Improvements in enzyme activity also includeincreases in stereoselectivity, sterospecificity, thermostability,solvent stability, or reduced product inhibition.

In some embodiments, the ketoreductase polypeptides of the invention areimproved as compared to SEQ ID NO:4, SEQ ID NO: 48, and/or SEQ ID NO:66with respect to their rate of enzymatic activity, i.e., their rate ofconverting the substrate to the product. In some embodiments, theketoreductase polypeptides are capable of converting the substrate tothe product at a rate that is at least 5-fold, 10-fold, 25-fold,50-fold, 75-fold, 100-fold, 150-fold, 200-fold, 250-fold, 300-fold,500-fold, or 1000-fold over the rate of SEQ ID NO:4 or SEQ ID NO:90.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, with apercent stereomeric excess of at least about 85% or with a percentstereomeric excess that is greater than the wild-type L. kefir KRED (SEQID NO:4). Exemplary polypeptides with this property include, but are notlimited to, polypeptides comprising amino acid sequences correspondingto SEQ ID NO: 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34,36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, and 62.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S, 3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, with apercent stereomeric excess of at least about 60-89% and at a rate thatis at least about 1-15 fold greater than the rate capable by thepolypeptide having the amino acid sequence of SEQ ID NO:48. Exemplarypolypeptides with this property include, but are not limited to,polypeptides comprising amino acid sequences corresponding to SEQ ID NO:6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40,42, 46, 50, 52, 54, 56, 58, 60, and 62. Because the referencepolypeptide having the amino acid sequence of SEQ ID NO:48 is capable ofconverting the substrate to the product at a rate (for example, 100%conversion in 20 hours of 1 g/L substrate with about 10 g/L of the KRED,in 50% IPA at pH 8) and with a steroselectivity that is improved overwild-type (SEQ ID NO:4), the polypeptides herein that are improved overSEQ ID NO:48 are also improved over wild-type.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S, 3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, with apercent stereomeric excess of at least about 90-94%. Exemplarypolypeptides with this property include, but are not limited to,polypeptides comprising amino acid sequences corresponding to SEQ ID NO:6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 40, 42,50, 52, 56, 58, 60, and 62.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S, 3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, with apercent stereomeric excess of at least about 95-99%. Exemplarypolypeptides with this property include, but are not limited to,polypeptides comprising amino acid sequences corresponding to SEQ ID NO:6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 42, 50, 52,56, 58, 60, and 62.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S, 3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, with apercent stereomeric excess of at least about 99%. Exemplary polypeptideswith this property include, but are not limited to, polypeptidescomprising amino acid sequences corresponding to SEQ ID NO:6, 8, 10, 12,14, 20, 22, 24, 30, 32, 34, 60, and 62.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S, 3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a ratethat is at least about 15-30 fold greater than the rate capable by thepolypeptide having the amino acid sequence of SEQ ID NO:48. Exemplarypolypeptides with this property include, but are not limited to,polypeptides comprising amino acid sequences corresponding to SEQ ID NO:6, 8, 10, 12, 14, 20, 22, 24, 26, 28, 30, 32, 34, 50, 60, and 62.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a ratethat is at least about 30-40 fold greater than the rate capable by thepolypeptide having the amino acid sequence of SEQ ID NO:48. Exemplarypolypeptides with this property include, but are not limited to,polypeptides comprising amino acid sequences corresponding to SEQ ID NO:6, 8, 10, 12, 14, 20, 22, 24, 26, 30, 34, 60, and 62.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a ratethat is at least about 40-50 fold greater than the rate capable by thepolypeptide having the amino acid sequence of SEQ ID NO:48. Exemplarypolypeptides with this property include, but are not limited to,polypeptides comprising amino acid sequences corresponding to SEQ ID NO:6, 8, 10, 12, 14, 22, and 60.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a ratethat is at least about 50 fold greater than the rate capable by thepolypeptide having the amino acid sequence of SEQ ID NO:48. Exemplarypolypeptides with this property include, but are not limited to,polypeptides comprising amino acid sequences corresponding to SEQ ID NO:6, 8, 10, and 12.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a ratethat is at least about 50 fold greater than the rate capable by thepolypeptide having the amino acid sequence of SEQ ID NO:48 and with astereomeric excess of at least 99%. Exemplary polypeptides with thisproperty include, but are not limited to, polypeptides comprising aminoacid sequences corresponding to SEQ ID NO: 6, 8, 10, and 12.

In some embodiments, the invention provides a ketoreductase polypeptidethat is capable of retaining its ability to convert the substrate,methyl-2-benzamidomethyl-3-oxobutyrate, to the product,2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, after heat treatmentat 40° C. for 21 hours. Exemplary polypeptides with this propertyinclude, but are not limited to, polypeptides comprising amino acidsequences corresponding to SEQ ID NO: 6, 10, and 44.

In another aspect, the present disclosure further provides ketoreductasepolypeptides capable of converting the substrate,methyl-2-benzamidomethyl-3-oxobutyrate, to the product,2R,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate. In some embodiments,these ketoreductases are capable of converting the substrate,methyl-2-benzamidomethyl-3-oxobutyrate, to the product,2R,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate with a percentstereomeric excess of at least about 85%. Exemplary polypeptidesinclude, but are not limited to, polypeptides comprising amino acidsequences corresponding to SEQ ID NO: 68, 72, 74, 76, 78, and 82.

In some embodiments, the 2R,3R selective ketoreductase polypeptide arecapable of converting the substrate,methyl-2-benzamidomethyl-3-oxobutyrate, to the product,2R,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a rate that is atleast about 1 fold greater than the rate capable by the polypeptidehaving the amino acid sequence of SEQ ID NO:66. Exemplary polypeptideswith this property include, but are not limited to, polypeptidescomprising amino acid sequences corresponding to SEQ ID NO: 64, 68, 70,72, 74, 76, 78. 80 and 82. Because the polypeptide having the amino acidsequence of SEQ ID NO:66 is capable of capable of converting thesubstrate, methyl-2-benzamidomethyl-3-oxobutyrate, to the product, 2R,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, with a stereomeric excessand at a rate that is greater than wild-type L. kefir KRED (SEQ IDNO:4), any polypeptide improved over SEQ ID NO:66 is also improved overwild-type L. kefir KRED.

In some embodiments, the 2R,2R selective ketoreductase polypeptide arecapable of converting the substrate,methyl-2-benzamidomethyl-3-oxobutyrate, to the product,2R,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a rate that is atleast about 1-2 fold greater than the rate capable by the polypeptidehaving the amino acid sequence of SEQ ID NO:66. Exemplary polypeptideswith this property include, but are not limited to, polypeptidescomprising amino acid sequences corresponding to SEQ ID NO: 64, 68, 70,72, 74, 76, 78. and 80.

In some embodiments, the 2R,2R selective ketoreductase polypeptides arecapable of converting the substrate,methyl-2-benzamidomethyl-3-oxobutyrate, to the product,2R,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a rate that is atleast about 5 fold greater than the rate capable by the polypeptidehaving the amino acid sequence of SEQ ID NO:66. Exemplary polypeptideswith this property include, but are not limited to, polypeptidescomprising amino acid sequences corresponding to SEQ ID NO: 64, 70, 72,76, 78. and 80.

In some embodiments, the 2R,2R selective ketoreductase polypeptides arecapable of converting the substrate,methyl-2-benzamidomethyl-3-oxobutyrate, to the product, 2R,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a rate that is atleast about 5 fold greater than the rate capable by the polypeptidehaving the amino acid sequence of SEQ ID NO:66 and with a stereomericexcess that is at least 85%. Exemplary polypeptides with this propertyinclude, but are not limited to, polypeptides comprising amino acidsequences corresponding to SEQ ID NO: 72 and 78.

In another aspect, the present disclosure provides polynucleotidesencoding the engineered ketoreductases described herein orpolynucleotides that hybridize to such polynucleotides under highlystringent conditions. The polynucleotide can include promoters and otherregulatory elements useful for expression of the encoded engineeredketoreductase, and can utilize codons optimized for specific desiredexpression systems. Exemplary polynucleotides include, but are notlimited to, SEQ ID NO: 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29,31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65,67, 69, 71, 73, 75, 77, 79, and 81. Exemplary polynucleotides alsoinclude polynucleotides encoding polypeptides that correspond to thesequence formulas of SEQ ID NO:83, 84, and 87.

In another aspect, the present disclosure provides host cells comprisingthe polynucleotides and/or expression vectors described herein. The hostcells may be L. kefir or L. brevis or L. minor, or they may be adifferent organism. The host cells can be used for the expression andisolation of the engineered ketoreductase enzymes described herein, or,alternatively, they can be used directly for the conversion of thesubstrate to the stereoisomeric product.

Whether carrying out the method with whole cells, cell extracts orpurified ketoreductase enzymes, a single ketoreductase enzyme may beused or, alternatively, mixtures of two or more ketoreductase enzymesmay be used.

As noted above, in some embodiments, the ketoreductase enzymes describedherein are capable of catalyzing the reduction reaction of the ketogroup in the compound of structural formula (I),methyl-2-benzamidomethyl-3-oxobutyrate (“the substrate”):

to the corresponding stereoisomeric alcohol product of structuralformula (II), 2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate (“theproduct”):

In some embodiments, the ketoreductase enzymes described herein arecapable of catalyzing the reduction reaction of the keto group in thecompound of structural formula (I) to the corresponding stereoisomericalcohol product of structural formula (III),2R,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, (which can also bereferred to as a “product”):

Accordingly, in some embodiments, provide herein are methods forreducing the substrate of the structural formula (I) to the alcoholproduct of structural formula (II) or structural formula (III), whichmethod comprises contacting or incubating the substrate with aketoreductase polypeptide of the disclosure under reaction conditionssuitable for reducing or converting the substrate to the product ofstructural formula (II) or structural formula (III).

In some embodiments, the product2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate of structural formula(II) can be used to synthesize intermediates and carbapenem compounds,as illustrated in Scheme 3:

Accordingly, in some embodiments, the ketoreductases of the disclosurecan be used in a method for the synthesis of the intermediate ofstructural formula (IVa),

where R¹ is H or a hydroxyl protecting group, and R¹⁰ is a halogen(e.g., Cl), or —OAc (Ac is acetate). Accordingly, in a method for thesynthesis of the intermediate of structural formula (IVa), a step in themethod comprises contacting or reacting the substrate of formula (I)with a ketoreductase of the disclosure under reaction conditionssuitable for reducing or converting the substrate to the product offormula (II).

In some embodiments, the ketoreductases of the disclosure can be use inthe synthesis of the intermediate of structural formula (VI):

where R² is H or a C1-C4 alkyl (e.g., —CH₃); R³ is H, or a hydroxylprotecting group; R⁴ is H, carboxy protecting group, ammonia group,alkali metal, or alkaline earth metal; and X is OH, or a leaving group.Exemplary leaving groups include, but are not limited to, —OP(O)(OR′) orOS(O2)R″, where R′ and R″ can be C1-C6 alkyl, C1-C6 alkaryl, aryl,perfluoro C1-C6 alkyl. Accordingly, in some embodiments, in a method forthe synthesis of the intermediate of formula (VI), a step in the methodcomprises contacting or reacting the substrate of formula (I) with aketoreductase of the disclosure under reaction conditions suitable forreducing or converting the substrate to the product of formula (II).

In some embodiments, the ketoreductases of the disclosure can be used inthe process for synthesis of carbapenem based therapeutic compound ofstructural formula (V):

or solvates, hydrates, salts, and prodrugs thereof, where R² is H or—CH₃; R⁵ can be various substituents, including, but not limited to,substituted or unsubstituted alkyl, substituted or unsubstituted aryl,substituted or unsubstituted heteroalkyl, substituted or unsubstitutedheterocycloalkyl, and substituted or unsubstituted heteroarylalkyl; andR⁶ is H, or a progroup, such as a hydrolyzable ester group. Accordingly,in the method for the synthesis of the compound of structural formula(V), a step in the method can comprise contacting or reacting thesubstrate of formula (I) with the ketoreductases of the disclosure underreaction conditions suitable for reducing or converting the substrate tothe product of formula (II). Exemplary carbapenems of structural formula(V) include, but are not limited to, Imipenem, Meropenem, Doripenem,Ertapenem, Biopenem, and Panipenem.

In some embodiments, the disclosure further provides use of theketoreductases in methods of synthesizing sulopenem compounds and in theintermediates used in the synthesis of sulopenems.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates the role of ketoreductases (KRED) in the conversionof the substrate compound of formula (I) to the corresponding product offormula (II). This reduction uses a KRED of the invention and aco-factor such as NADPH. Isopropyl alcohol (IPA) is used tocovert/recycle NADP⁺ to NADPH.

DETAILED DESCRIPTION 1.1 Definitions

As used herein, the following terms are intended to have the followingmeanings.

“Ketoreductase” and “KRED” are used interchangeably herein to refer to apolypeptide having an enzymatic capability of reducing a carbonyl groupto its corresponding alcohol. More specifically, the ketoreductasepolypeptides of the invention are capable of stereoselectively reducingthe compound of formula (I), supra to the corresponding product offormula (II), supra. The polypeptide typically utilizes a cofactorreduced nicotinamide adenine dinucleotide (NADH) or reduced nicotinamideadenine dinucleotide phosphate (NADPH) as the reducing agent.Ketoreductases as used herein include naturally occurring (wild type)ketoreductases as well as non-naturally occurring engineeredpolypeptides generated by human manipulation.

“Coding sequence” refers to that portion of a nucleic acid (e.g., agene) that encodes an amino acid sequence of a protein.

“Naturally-occurring” or “wild-type” refers to the form found in nature.For example, a naturally occurring or wild-type polypeptide orpolynucleotide sequence is a sequence present in an organism that can beisolated from a source in nature and which has not been intentionallymodified by human manipulation.

“Recombinant” when used with reference to, e.g., a cell, nucleic acid,or polypeptide, refers to a material, or a material corresponding to thenatural or native form of the material, that has been modified in amanner that would not otherwise exist in nature, or is identical theretobut produced or derived from synthetic materials and/or by manipulationusing recombinant techniques. Non-limiting examples include, amongothers, recombinant cells expressing genes that are not found within thenative (non-recombinant) form of the cell or express native genes thatare otherwise expressed at a different level.

“Percentage of sequence identity” and “percentage homology” are usedinterchangeably herein to refer to comparisons among polynucleotides andpolypeptides, and are determined by comparing two optimally alignedsequences over a comparison window, wherein the portion of thepolynucleotide or polypeptide sequence in the comparison window maycomprise additions or deletions (i.e., gaps) as compared to thereference sequence (which does not comprise additions or deletions) foroptimal alignment of the two sequences. The percentage may be calculatedby determining the number of positions at which the identical nucleicacid base or amino acid residue occurs in both sequences to yield thenumber of matched positions, dividing the number of matched positions bythe total number of positions in the window of comparison andmultiplying the result by 100 to yield the percentage of sequenceidentity. Alternatively, the percentage may be calculated by determiningthe number of positions at which either the identical nucleic acid baseor amino acid residue occurs in both sequences or a nucleic acid base oramino acid residue is aligned with a gap to yield the number of matchedpositions, dividing the number of matched positions by the total numberof positions in the window of comparison and multiplying the result by100 to yield the percentage of sequence identity. Those of skill in theart appreciate that there are many established algorithms available toalign two sequences. Optimal alignment of sequences for comparison canbe conducted, e.g., by the local homology algorithm of Smith andWaterman, 1981, Adv. Appl. Math. 2:482, by the homology alignmentalgorithm of Needleman and Wunsch, 1970, J. Mol. Biol. 48:443, by thesearch for similarity method of Pearson and Lipman, 1988, Proc. Natl.Acad. Sci. USA 85:2444, by computerized implementations of thesealgorithms (GAP, BESTFIT, FASTA, and TFASTA in the GCG WisconsinSoftware Package), or by visual inspection (see generally, CurrentProtocols in Molecular Biology, F. M. Ausubel et al., eds., CurrentProtocols, a joint venture between Greene Publishing Associates, Inc.and John Wiley & Sons, Inc., (1995 Supplement) (Ausubel)). Examples ofalgorithms that are suitable for determining percent sequence identityand sequence similarity are the BLAST and BLAST 2.0 algorithms, whichare described in Altschul et al., 1990, J. Mol. Biol. 215: 403-410 andAltschul et al., 1977, Nucleic Acids Res. 3389-3402, respectively.Software for performing BLAST analyses is publicly available through theNational Center for Biotechnology Information website. This algorithminvolves first identifying high scoring sequence pairs (HSPs) byidentifying short words of length W in the query sequence, which eithermatch or satisfy some positive-valued threshold score T when alignedwith a word of the same length in a database sequence. T is referred toas, the neighborhood word score threshold (Altschul et al, supra). Theseinitial neighborhood word hits act as seeds for initiating searches tofind longer HSPs containing them. The word hits are then extended inboth directions along each sequence for as far as the cumulativealignment score can be increased. Cumulative scores are calculatedusing, for nucleotide sequences, the parameters M (reward score for apair of matching residues; always >0) and N (penalty score formismatching residues; always <0). For amino acid sequences, a scoringmatrix is used to calculate the cumulative score. Extension of the wordhits in each direction are halted when: the cumulative alignment scorefalls off by the quantity X from its maximum achieved value; thecumulative score goes to zero or below, due to the accumulation of oneor more negative-scoring residue alignments; or the end of eithersequence is reached. The BLAST algorithm parameters W, T, and Xdetermine the sensitivity and speed of the alignment. The BLASTN program(for nucleotide sequences) uses as defaults a wordlength (W) of 11, anexpectation (E) of 10, M=5, N=−4, and a comparison of both strands. Foramino acid sequences, the BLASTP program uses as defaults a wordlength(W) of 3, an expectation (E) of 10, and the BLOSUM62 scoring matrix (seeHenikoff and Henikoff, 1989, Proc Natl Acad Sci USA 89:10915). Exemplarydetermination of sequence alignment and % sequence identity can employthe BESTFIT or GAP programs in the GCG Wisconsin Software package(Accelrys, Madison Wis.), using default parameters provided.

“Reference sequence” refers to a defined sequence used as a basis for asequence comparison. A reference sequence may be a subset of a largersequence, for example, a segment of a full-length gene or polypeptidesequence. Generally, a reference sequence is at least 20 nucleotide oramino acid residues in length, at least 25 residues in length, at least50 residues in length, or the full length of the nucleic acid orpolypeptide. Since two polynucleotides or polypeptides may each (1)comprise a sequence (i.e., a portion of the complete sequence) that issimilar between the two sequences, and (2) may further comprise asequence that is divergent between the two sequences, sequencecomparisons between two (or more) polynucleotides or polypeptide aretypically performed by comparing sequences of the two polynucleotidesover a “comparison window” to identify and compare local regions ofsequence similarity.

In some embodiments, a “reference sequence” can be based on a primaryamino acid sequence, where the reference sequence is a sequence that canhave one or more changes in the primary sequence. For instance, a“reference sequence based on SEQ ID NO:4 having at the residuecorresponding to X202 a leucine or valine” refers to a referencesequence in which the corresponding residue at X202 in SEQ ID NO:4 hasbeen changed to a leucine or valine.

“Comparison window” refers to a conceptual segment of at least about 20contiguous nucleotide positions or amino acids residues wherein asequence may be compared to a reference sequence of at least 20contiguous nucleotides or amino acids and wherein the portion of thesequence in the comparison window may comprise additions or deletions(i.e., gaps) of 20 percent or less as compared to the reference sequence(which does not comprise additions or deletions) for optimal alignmentof the two sequences. The comparison window can be longer than 20contiguous residues, and includes, optionally 30, 40, 50, 100, or longerwindows.

“Substantial identity” refers to a polynucleotide or polypeptidesequence that has at least 80 percent sequence identity, at least 85percent identity and 89 to 95 percent sequence identity, more usually atleast 99 percent sequence identity as compared to a reference sequenceover a comparison window of at least 20 residue positions, frequentlyover a window of at least 30-50 residues, wherein the percentage ofsequence identity is calculated by comparing the reference sequence to asequence that includes deletions or additions which total 20 percent orless of the reference sequence over the window of comparison. Inspecific embodiments applied to polypeptides, the term “substantialidentity” means that two polypeptide sequences, when optimally aligned,such as by the programs GAP or BESTFIT using default gap weights, shareat least 80 percent sequence identity, preferably at least 89 percentsequence identity, at least 95 percent sequence identity or more (e.g.,99 percent sequence identity). Preferably, residue positions which arenot identical differ by conservative amino acid substitutions.

“Corresponding to”, “reference to” or “relative to” when used in thecontext of the numbering of a given amino acid or polynucleotidesequence refers to the numbering of the residues of a specifiedreference sequence when the given amino acid or polynucleotide sequenceis compared to the reference sequence. In other words, the residuenumber or residue position of a given polymer is designated with respectto the reference sequence rather than by the actual numerical positionof the residue within the given amino acid or polynucleotide sequence.For example, a given amino acid sequence, such as that of an engineeredketoreductase, can be aligned to a reference sequence by introducinggaps to optimize residue matches between the two sequences. In thesecases, although the gaps are present, the numbering of the residue inthe given amino acid or polynucleotide sequence is made with respect tothe reference sequence to which it has been aligned.

“Stereoselectivity” refers to the preferential formation in a chemicalor enzymatic reaction of one stereoisomer over another.Stereoselectivity can be partial, where the formation of onestereoisomer is favored over the other, or it may be complete where onlyone stereoisomer is formed. When the stereoisomers are enantiomers, thestereoselectivity is referred to as enantioselectivity, the fraction(typically reported as a percentage) of one enantiomer in the sum ofboth. It is commonly alternatively reported in the art (typically as apercentage) as the enantiomeric excess (e.e.) calculated therefromaccording to the formula [major enantiomer−minor enantiomer]/[majorenantiomer+minor enantiomer]. Where the stereoisomers arediastereoisomers, the stereoselectivity is referred to asdiastereoselectivity, the fraction (typically reported as a percentage)of one diastereomer in a mixture of two diasteromers, commonlyalternatively reported as the diastereomeric excess (d.e.). Enantiomericexcess and diastereomeric excess are types of stereomeric excess.

“Highly stereoselective” refers to a ketoreductase polypeptide that iscapable of converting or reducing the substrate to the correspondingproduct having the chemical formula (II) or (III) with at least about85% stereomeric excess.

“Stereospecificity” refers to the preferential conversion in a chemicalor enzymatic reaction of one stereoisomer over another.Stereospecificity can be partial, where the conversion of onestereoisomer is favored over the other, or it may be complete where onlyone stereoisomer is converted.

“Chemoselectivity” refers to the preferential formation in a chemical orenzymatic reaction of one product over another.

“Improved enzyme property” refers to a ketoreductase polypeptide thatexhibits an improvement in any enzyme property as compared to areference ketoreductase. For the engineered ketoreductase polypeptidesdescribed herein, the comparison is generally made to the wild-typeketoreductase enzyme, although in some embodiments, the referenceketoreductase can be another improved engineered ketoreductase. Enzymeproperties for which improvement is desirable include, but are notlimited to, enzymatic activity (which can be expressed in terms ofpercent conversion of the substrate), thermal stability, solventstability, pH activity profile, cofactor requirements, refractoriness toinhibitors (e.g., product inhibition), stereospecificity, andstereoselectivity (including enantioselectivity).

“Increased enzymatic activity” refers to an improved property of theengineered ketoreductase polypeptides, which can be represented by anincrease in specific activity (e.g., product produced/time/weightprotein) or an increase in percent conversion of the substrate to theproduct (e.g., percent conversion of starting amount of substrate toproduct in a specified time period using a specified amount of KRED) ascompared to the reference ketoreductase enzyme. Exemplary methods todetermine enzyme activity are provided in the Examples. Any propertyrelating to enzyme activity may be affected, including the classicalenzyme properties of K_(m), V_(max), or k_(cat), changes of which canlead to increased enzymatic activity. Improvements in enzyme activitycan be from about 1.5 times the enzymatic activity of the correspondingwild-type ketoreductase enzyme, to as much as 2 times. 5 times, 10times, 20 times, 25 times, 50 times, 75 times, 100 times, or moreenzymatic activity than the naturally occurring ketoreductase or anotherengineered ketoreductase from which the ketoreductase polypeptides werederived. In specific embodiments, the engineered ketoreductase enzymeexhibits improved enzymatic activity in the range of 1.5 to 50 times,1.5 to 100 times greater than that of the parent ketoreductase enzyme.It is understood by the skilled artisan that the activity of any enzymeis diffusion limited such that the catalytic turnover rate cannot exceedthe diffusion rate of the substrate, including any required cofactors.The theoretical maximum of the diffusion limit, or k_(cat)/K_(m), isgenerally about 10⁸ to 10⁹ (M⁻¹ s⁻¹). Hence, any improvements in theenzyme activity of the ketoreductase will have an upper limit related tothe diffusion rate of the substrates acted on by the ketoreductaseenzyme. Ketoreductase activity can be measured by any one of standardassays used for measuring ketoreductase, such as a decrease inabsorbance or fluorescence of NADPH due to its oxidation with theconcomitant reduction of a ketone to an alcohol, or by product producedin a coupled assay. Comparisons of enzyme activities are made using adefined preparation of enzyme, a defined assay under a set condition,and one or more defined substrates, as further described in detailherein. Generally, when lysates are compared, the numbers of cells andthe amount of protein assayed are determined as well as use of identicalexpression systems and identical host cells to minimize variations inamount of enzyme produced by the host cells and present in the lysates.

“Conversion” refers to the enzymatic reduction of the substrate to thecorresponding product. “Percent conversion” refers to the percent of thesubstrate that is reduced to the product within a period of time underspecified conditions. Thus, the “enzymatic activity” or “activity” of aketoreductase polypeptide can be expressed as “percent conversion” ofthe substrate to the product.

“Thermostable” refers to a ketoreductase polypeptide that maintainssimilar activity (more than 60% to 80% for example) after exposure toelevated temperatures (e.g., 40-80° C.) for a period of time (e.g.,0.5-24 hrs) compared to the untreated enzyme.

“Solvent stable” refers to a ketoreductase polypeptide that maintainssimilar activity (more than e.g., 60% to 80%) after exposure to varyingconcentrations (e.g., 5-99%) of solvent (isopropylalcohol,tetrahydrofuran, 2-methyltetrahydrofuran, acetone, toluene,butylacetate, methyl tert-butylether, etc.) for a period of time (e.g.,0.5-24 hrs) compared to the untreated enzyme.

“pH stable” refers to a ketoreductase polypeptide that maintains similaractivity (more than e.g., 60% to 80%) after exposure to high or low pH(e.g., 4.5-6 or 8 to 12) for a period of time (e.g., 0.5-24 hrs)compared to the untreated enzyme.

“Thermo- and solvent stable” refers to a ketoreductase polypeptide thatare both thermostable and solvent stable.

“Derived from” as used herein in the context of engineered ketoreductaseenzymes, identifies the originating ketoreductase enzyme, and/or thegene encoding such ketoreductase enzyme, upon which the engineering wasbased. For example, the engineered ketoreductase enzyme of SEQ ID NO: 60was obtained by artificially evolving, over multiple generations thegene encoding the Lactobacillus kefir ketoreductase enzyme of SEQ IDNO:4. Thus, this engineered ketoreductase enzyme is “derived from” thewild-type ketoreductase of SEQ ID NO: 4.

“Hydrophilic amino acid or residue” refers to an amino acid or residuehaving a side chain exhibiting a hydrophobicity of less than zeroaccording to the normalized consensus hydrophobicity scale of Eisenberget al., 1984, J. Mol. Biol. 179:125-142. Genetically encoded hydrophilicamino acids include L-Thr (T), L-Ser (S), L-His (H), L-Glu (E), L-Asn(N), L-Gln (Q), L-Asp (D), L-Lys (K) and L-Arg (R).

“Acidic amino acid or residue” refers to a hydrophilic amino acid orresidue having a side chain exhibiting a pK value of less than about 6when the amino acid is included in a peptide or polypeptide. Acidicamino acids typically have negatively charged side chains atphysiological pH due to loss of a hydrogen ion. Genetically encodedacidic amino acids include L-Glu (E) and L-Asp (D).

“Basic amino acid or residue” refers to a hydrophilic amino acid orresidue having a side chain exhibiting a pK value of greater than about6 when the amino acid is included in a peptide or polypeptide. Basicamino acids typically have positively charged side chains atphysiological pH due to association with hydronium ion. Geneticallyencoded basic amino acids include L-Arg (R) and L-Lys (K).

“Polar amino acid or residue” refers to a hydrophilic amino acid orresidue having a side chain that is uncharged at physiological pH, butwhich has at least one bond in which the pair of electrons shared incommon by two atoms is held more closely by one of the atoms.Genetically encoded polar amino acids include L-Asn (N), L-Gln (Q),L-Ser (S) and L-Thr (T).

“Hydrophobic amino acid or residue” refers to an amino acid or residuehaving a side chain exhibiting a hydrophobicity of greater than zeroaccording to the normalized consensus hydrophobicity scale of Eisenberget al., 1984, J. Mol. Biol. 179:125-142. Genetically encoded hydrophobicamino acids include L-Pro (P), L-Ile (I), L-Phe (F), L-Val (V), L-Leu(L), L-Trp (W), L-Met (M), L-Ala (A) and L-Tyr (Y).

“Aromatic amino acid or residue” refers to a hydrophilic or hydrophobicamino acid or residue having a side chain that includes at least onearomatic or heteroaromatic ring. Genetically encoded aromatic aminoacids include L-Phe (F), L-Tyr (Y) and L-Trp (W). Although owing to thepKa of its heteroaromatic nitrogen atom L-His (H) it is sometimesclassified as a basic residue, or as an aromatic residue as its sidechain includes a heteroaromatic ring, herein histidine is classified asa hydrophilic residue or as a “constrained residue” (see below).

“Constrained amino acid or residue” refers to an amino acid or residuethat has a constrained geometry. Herein, constrained residues includeL-pro (P) and L-his (H). Histidine has a constrained geometry because ithas a relatively small imidazole ring. Proline has a constrainedgeometry because it also has a five membered ring.

“Non-polar amino acid or aesidue” refers to a hydrophobic amino acid orresidue having a side chain that is uncharged at physiological pH andwhich has bonds in which the pair of electrons shared in common by twoatoms is generally held equally by each of the two atoms (i.e., the sidechain is not polar). Genetically encoded non-polar amino acids includeL-Gly (G), L-Leu (L), L-Val (V), L-Ile (I), L-Met (M) and L-Ala (A).

“Aliphatic amino acid or residue” refers to a hydrophobic amino acid orresidue having an aliphatic hydrocarbon side chain. Genetically encodedaliphatic amino acids include L-Ala (A), L-Val (V), L-Leu (L) and L-Ile(I).

“Cysteine” or L-Cys (C) is unusual in that it can form disulfide bridgeswith other L-Cys (C) amino acids or other sulfanyl- orsulfhydryl-containing amino acids. The “cysteine-like residues” includecysteine and other amino acids that contain sulfhydryl moieties that areavailable for formation of disulfide bridges. The ability of L-Cys (C)(and other amino acids with —SH containing side chains) to exist in apeptide in either the reduced free —SH or oxidized disulfide-bridgedform affects whether L-Cys (C) contributes net hydrophobic orhydrophilic character to a peptide. While L-Cys (C) exhibits ahydrophobicity of 0.29 according to the normalized consensus scale ofEisenberg (Eisenberg et al., 1984, supra), it is to be understood thatfor purposes of the present disclosure L-Cys (C) is categorized into itsown unique group.

“Small amino acid or residue” refers to an amino acid or residue havinga side chain that is composed of a total three or fewer carbon and/orheteroatoms (excluding the α-carbon and hydrogens). The small aminoacids or residues may be further categorized as aliphatic, non-polar,polar or acidic small amino acids or residues, in accordance with theabove definitions. Genetically-encoded small amino acids include L-Ala(A), L-Val (V), L-Cys (C), L-Asn (N), L-Ser (S), L-Thr (T) and L-Asp(D).

“Hydroxyl-containing amino acid or residue” refers to an amino acidcontaining a hydroxyl (—OH) moiety. Genetically-encodedhydroxyl-containing amino acids include L-Ser (S) L-Thr (T) and L-Tyr(Y).

“Conservative” amino acid substitutions or mutations refer to theinterchangeability of residues having similar side chains, and thustypically involves substitution of the amino acid in the polypeptidewith amino acids within the same or similar defined class of aminoacids. However, as used herein, in some embodiments, conservativemutations do not include substitutions from a hydrophilic tohydrophilic, hydrophobic to hydrophobic, hydroxyl-containing tohydroxyl-containing, or small to small residue, if the conservativemutation can instead be a substitution from an aliphatic to analiphatic, non-polar to non-polar, polar to polar, acidic to acidic,basic to basic, aromatic to aromatic, or constrained to constrainedresidue. Further, as used herein, A, V, L, or I can be conservativelymutated to either another aliphatic residue or to another non-polarresidue. The table below shows exemplary conservative substitutions.

TABLE 1 Residue Possible Conservative Mutations A, L, V, I Otheraliphatic (A, L, V, I) Other non-polar (A, L, V, I, G, M) G, M Othernon-polar (A, L, V, I, G, M) D, E Other acidic (D, E) K, R Other basic(K, R) P, H Other constrained (P, H) N, Q, S, T Other polar Y, W, FOther aromatic (Y, W, F) C None

“Non-conservative substitution” refers to substitution or mutation of anamino acid in the polypeptide with an amino acid with significantlydiffering side chain properties. Non-conservative substitutions may useamino acids between, rather than within, the defined groups listedabove. In one embodiment, a non-conservative mutation affects (a) thestructure of the peptide backbone in the area of the substitution (e.g.,proline for glycine) (b) the charge or hydrophobicity, or (c) the bulkof the side chain.

“Deletion” refers to modification to the polypeptide by removal of oneor more amino acids from the reference polypeptide. Deletions cancomprise removal of 1 or more amino acids, 2 or more amino acids, 5 ormore amino acids, 10 or more amino acids, 15 or more amino acids, or 20or more amino acids, up to 10% of the total number of amino acids, up to20% of the total number of amino acids, or up to 30% of the total numberof amino acids making up the polypeptide while retaining enzymaticactivity and/or retaining the improved properties of an engineeredketoreductase enzyme. Deletions can be directed to the internal portionsand/or terminal portions of the polypeptide. In various embodiments, thedeletion can comprise a continuous segment or can be discontinuous.

“Insertion” refers to modification to the polypeptide by addition of oneor more amino acids from the reference polypeptide. In some embodiments,the improved engineered ketoreductase enzymes comprise insertions of oneor more amino acids to the naturally occurring ketoreductase polypeptideas well as insertions of one or more amino acids to other improvedketoreductase polypeptides. Insertions can be in the internal portionsof the polypeptide, or to the carboxy or amino terminus. Insertions asused herein include fusion proteins as is known in the art. Theinsertion can be a contiguous segment of amino acids or separated by oneor more of the amino acids in the naturally occurring polypeptide.

“Fragment” as used herein refers to a polypeptide that has anamino-terminal and/or carboxy-terminal deletion, but where the remainingamino acid sequence is identical to the corresponding positions in thesequence. Fragments can be at least 14 amino acids long, at least 20amino acids long, at least 50 amino acids long or longer, and up to 70%,80%, 90%, 95%, 98%, and 99% of the full-length ketoreductasepolypeptide, for example the polypeptide of SEQ ID NO:2, 4 or 86.

“Isolated polypeptide” refers to a polypeptide which is substantiallyseparated from other contaminants that naturally accompany it, e.g.,protein, lipids, and polynucleotides. The term embraces polypeptideswhich have been removed or purified from their naturally-occurringenvironment or expression system (e.g., host cell or in vitrosynthesis). The improved ketoreductase enzymes may be present within acell, present in the cellular medium, or prepared in various forms, suchas lysates or isolated preparations. As such, in some embodiments, theimproved ketoreductase enzyme can be an isolated polypeptide.

“Substantially pure polypeptide” refers to a composition in which thepolypeptide species is the predominant species present (i.e., on a molaror weight basis it is more abundant than any other individualmacromolecular species in the composition), and is generally asubstantially purified composition when the object species comprises atleast about 50 percent of the macromolecular species present by mole or% weight. Generally, a substantially pure ketoreductase composition willcomprise about 60% or more, about 70% or more, about 80% or more, about90% or more, about 95% or more, and about 98% or more of allmacromolecular species by mole or % weight present in the composition.In some embodiments, the object species is purified to essentialhomogeneity (i.e., contaminant species cannot be detected in thecomposition by conventional detection methods) wherein the compositionconsists essentially of a single macromolecular species. Solventspecies, small molecules (<500 Daltons), and elemental ion species arenot considered macromolecular species. In some embodiments, the isolatedimproved ketoreductases polypeptide is a substantially pure polypeptidecomposition.

“Stringent hybridization” is used herein to refer to conditions underwhich nucleic acid hybrids are stable. As known to those of skill in theart, the stability of hybrids is reflected in the melting temperature(T_(m)) of the hybrids. In general, the stability of a hybrid is afunction of ion strength, temperature, G/C content, and the presence ofchaotropic agents. The T_(m) values for polynucleotides can becalculated using known methods for predicting melting temperatures (see,e.g., Baldino et al., Methods Enzymology 168:761-777; Bolton et al.,1962, Proc. Natl. Acad. Sci. USA 48:1390; Bresslauer et al., 1986, Proc.Natl. Acad. Sci USA 83:8893-8897; Freier et al., 1986, Proc. Natl. Acad.Sci USA 83:9373-9377; Kierzek et al., Biochemistry 25:7840-7846; Rychliket al., 1990, Nucleic Acids Res 18:6409-6412 (erratum, 1991, NucleicAcids Res 19:698); Sambrook et al., supra); Suggs et al., 1981, InDevelopmental Biology Using Purified Genes (Brown et al., eds.), pp.683-693, Academic Press; and Wetmur, 1991, Crit Rev Biochem Mol Biol26:227-259. All publications incorporate herein by reference). In someembodiments, the polynucleotide encodes the polypeptide disclosed hereinand hybridizes under defined conditions, such as moderately stringent orhighly stringent conditions, to the complement of a sequence encoding anengineered ketoreductase enzyme of the present disclosure.

“Hybridization stringency” relates to hybridization conditions, such aswashing conditions, in the hybridization of nucleic acids. Generally,hybridization reactions are performed under conditions of lowerstringency, followed by washes of varying but higher stringency. Theterm “moderately stringent hybridization” refers to conditions thatpermit target-DNA to bind a complementary nucleic acid that has about60% identity, preferably about 75% identity, about 85% identity to thetarget DNA; with greater than about 90% identity totarget-polynucleotide. Exemplary moderately stringent conditions areconditions equivalent to hybridization in 50% formamide, 5×Denhart'ssolution, 5×SSPE, 0.2% SDS at 42° C., followed by washing in 0.2×SSPE,0.2% SDS, at 42° C. “High stringency hybridization” refers generally toconditions that are about 10° C. or less from the thermal meltingtemperature T_(m) as determined under the solution condition for adefined polynucleotide sequence. In some embodiments, a high stringencycondition refers to conditions that permit hybridization of only thosenucleic acid sequences that form stable hybrids in 0.018M NaCl at 65° C.(i.e., if a hybrid is not stable in 0.018M NaCl at 65° C., it will notbe stable under high stringency conditions, as contemplated herein).High stringency conditions can be provided, for example, byhybridization in conditions equivalent to 50% formamide, 5×Denhart'ssolution, 5×SSPE, 0.2% SDS at 42° C., followed by washing in 0.1×SSPE,and 0.1% SDS at 65° C. Another high stringency condition is hybridizingin conditions equivalent to hybridizing in 5×SSC containing 0.1% (w:v)SDS at 65° C. and washing in 0.1×SSC containing 0.1% SDS at 65° C. Otherhigh stringency hybridization conditions, as well as moderatelystringent conditions, are described in the references cited above.

“Heterologous” polynucleotide refers to any polynucleotide that isintroduced into a host cell by laboratory techniques, and includespolynucleotides that are removed from a host cell, subjected tolaboratory manipulation, and then reintroduced into a host cell.

“Codon optimized” refers to changes in the codons of the polynucleotideencoding a protein to those preferentially used in a particular organismsuch that the encoded protein is efficiently expressed in the organismof interest. Although the genetic code is degenerate in that most aminoacids are represented by several codons, called “synonyms” or“synonymous” codons, it is well known that codon usage by particularorganisms is nonrandom and biased towards particular codon triplets.This codon usage bias may be higher in reference to a given gene, genesof common function or ancestral origin, highly expressed proteins versuslow copy number proteins, and the aggregate protein coding regions of anorganism's genome. In some embodiments, the polynucleotides encoding theketoreductases enzymes may be codon optimized for optimal productionfrom the host organism selected for expression.

“Preferred, optimal, high codon usage bias codons” refersinterchangeably to codons that are used at higher frequency in theprotein coding regions than other codons that code for the same aminoacid. The preferred codons may be determined in relation to codon usagein a single gene, a set of genes of common function or origin, highlyexpressed genes, the codon frequency in the aggregate protein codingregions of the whole organism, codon frequency in the aggregate proteincoding regions of related organisms, or combinations thereof. Codonswhose frequency increases with the level of gene expression aretypically optimal codons for expression. A variety of methods are knownfor determining the codon frequency (e.g., codon usage, relativesynonymous codon usage) and codon preference in specific organisms,including multivariat analysis, for example, using cluster analysis orcorrespondence analysis, and the effective number of codons used in agene (see GCG CodonPreference, Genetics Computer Group WisconsinPackage; CodonW, John Peden, University of Nottingham; McInerney, J. O,1998, Bioinformatics 14:372-73; Stenico et al., 1994, Nucleic Acids Res.222437-46; Wright, F., 1990, Gene 87:23-29). Codon usage tables areavailable for a growing list of organisms (see for example, Wada et al.,1992, Nucleic Acids Res. 20:2111-2118; Nakamura et al., 2000, Nucl.Acids Res. 28:292; Duret, et al., supra; Henaut and Danchin,“Escherichia coli and Salmonella,” 1996, Neidhardt, et al. Eds., ASMPress, Washington D.C., p. 2047-2066. The data source for obtainingcodon usage may rely on any available nucleotide sequence capable ofcoding for a protein. These data sets include nucleic acid sequencesactually known to encode expressed proteins (e.g., complete proteincoding sequences-CDS), expressed sequence tags (ESTS), or predictedcoding regions of genomic sequences (see for example, Mount, D.,Bioiuformatics: Sequence and Genome Analysis, Chapter 8, Cold SpringHarbor Laboratory Press, Cold Spring Harbor, N.Y., 2001; Uberbacher, E.C., 1996, Methods Enzymol. 266:259-281; Tiwari et al., 1997, Comput.Appl. Biosci. 13:263-270).

“Control sequence” is defined herein to include all components, whichare necessary or advantageous for the expression of a polypeptide of thepresent disclosure. Each control sequence may be native or foreign tothe nucleic acid sequence encoding the polypeptide. Such controlsequences include, but are not limited to, a leader, polyadenylationsequence, propeptide sequence, promoter, signal peptide sequence, andtranscription terminator.

“Operably linked” is defined herein as a configuration in which acontrol sequence is appropriately placed (i.e., in a functionalrelationship) at a position relative to a polynucleotide of interestsuch that the control sequence directs or regulates the expression ofthe polynucleotide and/or polypeptide of interest.

“Promoter sequence” is a nucleic acid sequence that is recognized by ahost cell for expression of a polynucleotide of interest, such as acoding sequence. The control sequence may comprise an appropriatepromoter sequence. The promoter sequence contains transcriptionalcontrol sequences, which mediate the expression of a polynucleotide ofinterest. The promoter may be any nucleic acid sequence which showstranscriptional activity in the host cell of choice including mutant,truncated, and hybrid promoters, and may be obtained from genes encodingextracellular or intracellular polypeptides either homologous orheterologous to the host cell.

1.2 Ketoreductase Enzymes

In one aspect, the present disclosure provides engineered ketoreductase(“KRED”) enzymes that are capable of stereoselectively reducing orconverting the racemic mixture of methyl-2-benzamidomethyl-3-oxobutyrate(“the substrate”) to 2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate(“the 2S,3R product”). These ketoreductase polypeptides (also describedherein as “2S,3R selective ketoreductases”) have an improved propertyfor reducing or converting methyl-2-benzamidomethyl-3-oxobutyrate to 2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate when compared with thenaturally-occurring, wild-type KRED enzyme obtained from L. kefir (SEQID NO:4), L. brevis (SEQ ID NO:2), or L. minor (SEQ ID NO:86) or whencompared with other engineered ketoreductase enzymes.

In some embodiments, the improved property as compared to wild-type oranother engineered polypeptide, such as SEQ ID NO:64, is with respect toincrease in stereoselectivity for reducing or converting the substratemethyl-2-benzamidomethyl-3-oxobutyrate to2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, i.e., herein, anincrease in the stereomeric excess of the product. In some embodiments,the improved property of the ketoreductase polypeptide is with respectto an increase in its ability to convert or reduce a greater percentageof the substrate to the product. In some embodiments, the improvedproperty of the ketoreductase polypeptide is with respect to an increasein its rate of conversion of the substrate to the product, which can bemanifested by the ability to use less of the improved polypeptide ascompared to the wild-type or other reference sequence to reduce orconvert the same amount of product. In some embodiments, the improvedproperty of the ketoreductase polypeptide is with respect to itsstability or thermostability. In some embodiments, the ketoreductasepolypeptide has more than one improved property, such as increasedstereoselectivity and improved enzymatic activity.

The present disclosure further provides engineered ketoreductase enzymesthat are capable of stereoselectively reducing or converting a racemicmixture of methyl-2-benzamidomethyl-3-oxobutyrate (“the substrate) to2R, 3R-methyl-2-benzamidomethyl-3-hydroxybutyrate (“the 2R,3R product”).Similar to the engineered polypeptides that produce the 2S,3R product,the engineered ketoreductases capable of producing the 2R,3R product(also described herein as 2R,3R selective ketoreductases) have animproved property as compared to wild-type or another engineeredpolypeptide, such as SEQ ID NO:66. In some embodiments, the improvedproperty is with respect to the stereoselectivity for reducing orconverting the substrate methyl-2-benzamidomethyl-3-oxobutyrate to 2R,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate. In some embodiments, theimproved property is with respect to it enzymatic activity for reducingthe substrate to the 2R, 3R product. In some embodiments, the improvedproperty of the ketoreductase polypeptide is with respect to itsstability or thermostability. In some embodiments, the ketoreductasepolypeptide has more than one improved property, such as increasedstereoselectivity and improved enzymatic activity.

As described in more detail below, the ketoreductase polypeptidescapable of converting the substrate to the 2S,3R product comprise anamino acid sequence in which the residue corresponding to X202 of SEQ IDNO:2, 4, or 86 is valine or leucine. In some embodiments, theketoreductase polypeptides comprise an amino acid sequence in which theresidue corresponding to X94 of SEQ ID NO:2, 4, or 86 is an aliphatic orpolar residue, particularly alanine or threonine; and the residuecorresponding to X202 of SEQ ID NO:2, 4, or 86 is valine or leucine. Insome embodiments, the 2S,3R selective ketoreductase polypeptidescomprise an amino acid sequence in which the residue corresponding toX94 of SEQ ID NO:2, 4, or 86 is an aliphatic or polar residue,particularly alanine or threonine; residue corresponding to X199 of SEQID NO:2. 4. or 86 is a constrained, polar, or aliphatic residue,particularly histidine, asparagine, or alanine; and residuecorresponding to X202 of SEQ ID NO:2, 4, or 86 is valine or leucine.

As noted above, the ketoreductases of the disclosure can be described inreference to the amino acid sequence of a naturally occurringketoreductase of L. kefir, L. brevis, or L. minor (also referred to as“ADH” or “alcohol dehydrogenase”) or another engineered ketoreductase.As such, the amino acid residue position is determined in theketoreductases beginning from the initiating methionine (M) residue(i.e., M represents residue position 1), although it will be understoodby the skilled artisan that this initiating methionine residue may beremoved by biological processing machinery, such as in a host cell or invitro translation system, to generate a mature protein lacking theinitiating methionine residue. The amino acid residue position at whicha particular amino acid or amino acid change is present in an amino acidsequence is sometimes describe herein in terms “Xn”, or “position n”,where n refers to the residue position. Where the amino acid residues atthe same residue position differ between the ketoreductases, thedifferent residues may be denoted by an “/” with the arrangement being“kefir residue/brevis residue/minor”. A substitution mutation, which isa replacement of an amino acid residue in a reference sequence, forexample the wildtype ketoreductases of SEQ ID NO:2 and SEQ ID NO:4 andSEQ ID NO:86, with a different amino acid residue may be denoted by thesymbol “→”. Herein, in some embodiments, mutations are sometimesdescribed as a mutation “to a” type of amino acid. For example, residue199 of SEQ ID NO:4 can be mutated “to a” polar residue. But the use ofthe phrase “to a” does not exclude mutations from one amino acid of aclass to another amino acid of the same class. For example, residue 199of SEQ ID NO:4 is an aliphatic residue, leucine, but it can be mutatedto a different aliphatic residue, for example, the mutation can be a“L199A” (199→A) mutation. The amino acid sequence of the naturallyoccurring ketoreductase (also referred to as “ADH” or “alcoholdehydrogenase”) of L. kefir, L. brevis, or of L. minor, can be obtainedfrom the polynucleotide known to encode the ketoreductase activity(e.g., Genbank accession no. AAP94029 GI:33112056 or SEQ ID NO:3 for L.kefir; Genbank accession no. CAD66648 GI:28400789 or SEQ ID NO:1 for L.brevis; and SEQ ID NO:86 for L. minor).

In some embodiments, the ketoreductase polypeptides herein can have anumber of modifications to the reference sequence (e.g., naturallyoccurring polypeptide or an engineered polypeptide) to result in theimproved ketoreductase property. As used herein, “modifications” includeamino acid substitutions, deletions, and insertions. Any one or acombination of modifications can be introduced into the naturallyoccurring or engineered polypeptide to generate engineered enzymes. Insuch embodiments, the number of modifications to the amino acid sequencecan comprise one or more amino acids, 2 or more amino acids, 3 or moreamino acids, 4 or more amino acids, 5 or more amino acids, 6 or moreamino acids, 8 or more amino acids, 10 or more amino acids, 15 or moreamino acids, or 20 or more amino acids, up to 10% of the total number ofamino acids, up to 10% of the total number of amino acids, up to 15% ofthe total number of amino acids, up to 20% of the total number of aminoacids, or up to 30% of the total number of amino acids of the referencepolypeptide sequence. In some embodiments, the number of modificationsto the naturally occurring polypeptide or an engineered polypeptide thatproduces an improved ketoreductase property may comprise from about 1-2,1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16,1-18, 1-20, 1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 modifications ofthe reference sequence. In some embodiments, the number of modificationscan be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22,24, 26, 30, 35 or about 40 amino acid residues. The modifications cancomprise insertions, deletions, substitutions, or combinations thereof.

In some embodiments, the modifications comprise amino acid substitutionsto the reference sequence. Substitutions that can produce an improvedketoreductase property may be at one or more amino acids, 2 or moreamino acids, 3 or more amino acids, 4 or more amino acids, 5 or moreamino acids, 6 or more amino acids, 8 or more amino acids, 10 or moreamino acids, 15 or more amino acids, or 20 or more amino acids, up to10% of the total number of amino acids, up to 10% of the total number ofamino acids, up to 20% of the total number of amino acids, or up to 30%of the total number of amino acids of the reference enzyme sequence. Insome embodiments, the number of substitutions to the naturally occurringpolypeptide or an engineered polypeptide that produces an improvedketoreductase property can comprise from about 1-2, 1-3, 1-4, 1-5, 1-6,1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20, 1-22,1-24, 1-26, 1-30, 1-35 or about 1-40 amino acid substitutions of thereference sequence. In some embodiments, the number of substitutions canbe 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24,26, 30, 35 or about 40 amino acid residues.

In some embodiments, the improved ketoreductase polypeptide comprises anamino acid sequence that is at least about 85%, 86%, 87%, 88%, 89%, 90%,91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% or more identical to areference sequence based on SEQ ID NO:2, 4, or 86 having at the residuecorresponding to X202 a leucine or valine, with the proviso that theketoreductase polypeptide has an amino acid sequence in which theresidue corresponding to X202 is leucine or valine. In some embodiments,the residue corresponding to X202 is leucine. In some embodiments, theseketoreductase polypeptides can have one or more residue differences atother residue positions as compared to the reference amino acidsequence. The differences include various modifications, such assubstitutions, deletions, and insertions. The substitutions can benon-conservative substitutions, conservative substitutions, or acombination of non-conservative and conservative substitutions. In someembodiments, these ketoreductase polypeptides can have optionally fromabout 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14,1-15, 1-16, 1-18, 1-20, 1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40residue differences at other amino acid residues as compared to thereference sequence. In some embodiments, the number of difference can be1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24, 26,30, 35 or about 40 residue differences at other amino acid residues ascompared to the reference sequence. In some embodiments, the referencesequence is SEQ ID NO:48.

In some embodiments, the improved ketoreductase polypeptide comprises anamino acid sequence that is at least about 85%, 86%, 87%, 88%, 89%, 90%,91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% or more identical to areference sequence based on SEQ ID NO:2, 4 or 86 having the followingfeatures: residue corresponding to X94 is an aliphatic or polar residue,particularly alanine or threonine; and residue corresponding to X202 isvaline or leucine; with the proviso that the ketoreductase polypeptidehas an amino acid sequence having at least the preceding features (i.e.,the residue corresponding to X94 is an aliphatic or polar residue, andthe residue corresponding to X202 is valine or leucine). In someembodiments, the ketoreductase has an amino acid sequence in which theresidue corresponding to X94 is a polar residue, and the residuecorresponding to X202 is valine or leucine. In some embodiments, theketoreductase has an amino acid sequence in which the residuecorresponding to X94 is threonine and the residue corresponding to X202is valine or leucine. In some embodiments, these ketoreductasepolypeptides can have optionally from about 1-2, 1-3, 1-4, 1-5, 1-6,1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20, 1-22,1-24, 1-26, 1- 30, 1-35 or about 1-40 residue differences at other aminoacid residue positions as compared to the reference sequence. In someembodiments, the number of difference can be 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 14, 15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40 residuedifferences at other amino acid residues as compared to the referencesequence. In some embodiments, the reference sequence is SEQ ID NO:26 or28.

In some embodiments, the improved ketoreductase polypeptide comprises anamino acid sequence that is at least about 85%, 86%, 87%, 88%, 89%, 90%,91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% or more identical to areference sequence based on SEQ ID NO:2, 4 or 86 having the followingfeatures: residue corresponding to X94 is an aliphatic or polar residue,particularly alanine or threonine; residue corresponding to X199 is analiphatic, constrained or polar residue, particularly alanine,asparagine, or histidine; and residue corresponding to X202 is valine orleucine; with the proviso that the ketoreductase polypeptide has anamino acid sequence having at least the preceding features (i.e., theresidue corresponding to X94 is an aliphatic or polar residue; theresidue corresponding to X199 is an aliphatic, constrained or polarresidue; and the residue corresponding to X202 is valine or leucine). Insome embodiments, the residue corresponding to X94 is a polar residue;the residue corresponding to X199 is an aliphatic, constrained or polarresidue; and the residue corresponding to X202 is valine or leucine. Insome embodiments, the ketoreductase has an amino acid sequence in whichthe residue corresponding to X94 is threonine; residue corresponding toX199 is alanine, asparagine, or histidine; and the residue correspondingto X202 is valine or leucine. In some embodiments, these ketoreductasepolypeptides can have one or more residue differences at other residuepositions as compared to the reference amino acid sequence. Thedifferences include various modifications, such as substitutions,deletions, and insertions. The substitutions can be non-conservativesubstitutions, conservative substitutions, or a combination ofnon-conservative and conservative substitutions. In some embodiments,these ketoreductase polypeptides can have optionally from about 1-2,1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16,1-18, 1-20, 1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residuedifferences at other amino acid residue positions as compared to thereference sequence. In some embodiments, the number of difference can be1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24, 26,30, 35 or about 40 residue differences at other amino acid residues ascompared to the reference sequence. In some embodiments, the referencesequence is SEQ ID NO:22, 24 or 30.

In view of the foregoing, the 2S,3R selective ketoreductases can bedescribed with respect to features of the various combinations ofresidues corresponding to X94, X199, and X202. For instance, a 2S,3Rselective polypeptide characterized by features at residuescorresponding to X94 and X202 refer to the descriptions provided hereinfor the combination of the specified residue positions. Similarly, a2S,3R selective polypeptide characterized by features at residuescorresponding to X94, X199, and X202 refer to the descriptions providedherein for the combination of the specified residues. As furtherdescribed below, these ketoreductases can have one or more additionalfeatures in the amino acid sequence as compared to a reference sequence.

In some embodiments, a 2S,3R selective ketoreductase polypeptidecomprises an amino acid sequence based on the sequence formulas as laidout in SEQ ID NO:83, SEQ ID NO:84, or SEQ ID NO:87 (or a region thereof,such as residues 90-211). SEQ ID NO:84 is based on the wild-type aminoacid sequence of the L. kefir ketoreductase (SEQ ID NO:4), SEQ ID NO:83is based on the wild-type amino acid sequence of the L. brevisketoreductase (SEQ ID NO:2), and SEQ ID NO:87 is based on the wild-typeamino acid sequence of the L minor ketoreductase (SEQ ID NO:86). SEQ IDNO:83, 84 or 87 specify that the residue corresponding to X94 is analiphatic or polar residue; residue corresponding to X199 is analiphatic, constrained or polar residue; and residue corresponding toX202 is valine or leucine. The sequence formula further specifiesfeatures for various other residue positions, as described below.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, can have one or more additional featuresselected from the following: residue corresponding to X2 is a polar,non-polar, or aliphatic residue; residue corresponding to X4 is a basicresidue or cysteine; residue corresponding to X11 is a non-polar,aliphatic, or aromatic residue; residue corresponding to X40 is aconstrained or basic residue; residue corresponding to X80 is anon-polar, aliphatic, or polar residue; residue corresponding to X86 isa non-polar, aliphatic, or polar residue; residue corresponding to X96is a polar, aromatic, non-polar, or aliphatic residue; residuecorresponding to X105 is a non-polar, aliphatic, basic or acidicresidue; residue corresponding to X129 is a non-polar or polar residue;residue corresponding to X147 is an aromatic, non-polar or aliphaticresidue; residue corresponding to X153 is a polar, non-polar oraliphatic residue; residue corresponding to X190 is an aromatic orconstrained residue; residue corresponding to X195 is a non-polar oraliphatic residue; residue corresponding to X196 is a non-polar oraliphatic residue; residue corresponding to X206 is a non-polar oraromatic residue; residue corresponding to X226 is a non-polar oraliphatic residue; residue corresponding to X248 is a non-polar or basicresidue; residue corresponding to X249 is an aromatic residue. In someembodiments, the amino acid sequence can have at least two, three, four,five, six or more of the features. In some embodiments, the polypeptidescomprising an amino acid sequence that is based on the sequence formulaof SEQ ID NO:83, 84 or 87 (or region thereof) can have additionally oneor more residue differences at residue positions not specified by an Xabove as compared to the reference sequence of SEQ ID NO:2, 4 or 86. Insome embodiments, the differences can be 1-2, 1-3, 1-4, 1-5, 1-6, 1-7,1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20, 1-22, 1-24,1-26, 1-30, 1-35 or about 1-40 residue differences at other amino acidresidue positions not defined by X above. In some embodiments, thenumber of differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14,15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40 residue differences atother amino acid residue positions. In some embodiments, the differencescomprise conservative mutations.

In some embodiments, the polypeptides comprising an amino acid sequencebased on the sequence formula of SEQ ID NO:83, 84 or 87, or regionthereof, such as residues 90-211, can have one or more conservativemutations as compared to the amino acid sequences of SEQ ID NO: 2, 4 or86. Exemplary conservative mutations include amino acid replacementssuch as, but not limited to: replacement of residue corresponding to X21valine (V) with another aliphatic residue, e.g., isoleucine; replacementof residue corresponding to X78 glutamic acid (E) with another acidicresidue, e.g., aspartic acid; replacement of residue corresponding toX145 glutamic acid (E) with another acidic residue, e.g., aspartic acid;replacement of residue corresponding to X153 leucine (L) with anotheraliphatic residue, e.g., alanine; replacement of residue correspondingto X195 leucine (L) with another aliphatic residue, e.g., valine;replacement of residue corresponding to X196 with another aliphaticresidue, e.g., leucine; replacement of residue corresponding to X226isoleucine (I) with another aliphatic residue, e.g., valine.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, can have one or more additional featuresselected from the following: residue corresponding to X2 is a serine,threonine, glutamine, or asparagine, glycine, methionine, alanine,valine, leucine, or isoleucine, particularly serine, threonine, oralanine; residue corresponding to X4 is an arginine, or lysine, orcysteine, particularly arginine or cysteine; residue corresponding toX11 is a glycine, methionine, alanine, valine, leucine, isoleucine,tyrosine, phenylalanine, or tryptophan, particularly isoleucine,leucine, or phenylalanine; residue corresponding to X40 is proline,histidine, arginine, or lysine, particularly histidine or arginine;residue corresponding to X80 is glycine, methionine, alanine, valine,leucine, isoleucine, serine, threonine, glutamine, or asparagine,particularly alanine or threonine; residue corresponding to X86 isserine, threonine, glutamine, asparagine, glycine, methionine, alanine,valine, leucine, or isoleucine, particularly threonine or isoleucine;residue corresponding to X96 is serine, threonine, glutamine,asparagine, glycine, methionine, alanine, valine, leucine, isoleucine,tyrosine, phenylalanine, or tryptophan, particularly serine, asparagine,valine, or phenylalanine; residue corresponding to X105 is glycine,methionine, alanine, valine, leucine, isoleucine, arginine, lysine,aspartic acid, or glutamic acid, particularly glutamic acid, lysine,alanine, or glycine; residue corresponding to X129 is glycine,methionine, alanine, valine, leucine, isoleucine, serine, threonine,glutamine, or asparagine, particularly methionine or threonine; residuecorresponding to X147 is tyrosine, phenylalanine, tryptophan, glycine,methionine, alanine, valine, leucine, or isoleucine, particularlyphenylalanine, methionine, or leucine; residue corresponding to X153 isa serine, threonine, glutamine, asparagine, glycine, methionine,alanine, valine, leucine, or isoleucine, particularly leucine, alanine,or serine; residue corresponding to X190 is tyrosine, phenylalanine,tryptophan, histidine, or proline, particularly tyrosine, histidine orproline; residue corresponding to X195 is glycine, methionine, alanine,valine, leucine, or isoleucine, particularly leucine or valine; residuecorresponding to X196 is glycine, methionine, alanine, valine, leucine,or isoleucine, particularly leucine; residue corresponding to X206 isglycine, methionine, alanine, valine, leucine, isoleucine, tyrosine,phenylalanine, or tryptophan, particularly methionine or phenylalanine;residue corresponding to X226 is glycine, methionine, alanine, valine,leucine or isoleucine, particularly isoleucine or valine; residuecorresponding to X248 is glycine, methionine, alanine, valine, leucine,isoleucine, lysine, or arginine, particularly glycine, lysine, orarginine; and residue corresponding to X249 is tyrosine, phenylalanine,or tryptophan, particularly tyrosine or tryptophan. In some embodiments,the amino acid sequence can have at least two, three, four, five, six ormore of the features. In some embodiments, the polypeptides comprisingan amino acid sequence that is based on the sequence formula of SEQ IDNO:83, 84 or 87 (or region thereof) can have additionally one or moreresidue differences at residue positions not specified by an X above ascompared to the reference sequence of SEQ ID NO:2, 4 or 86. In someembodiments, the differences can be 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8,1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20, 1-22, 1-24, 1-26,1-30, 1-35 or about 1-40 residue differences at other amino acid residuepositions not defined by X above. In some embodiments, the number ofdifferences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16,18, 20, 22, 24, 26, 30, 35 or about 40 residue differences at otheramino acid residue positions. In some embodiments, the differencescomprise conservative mutations.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, can have additionally one or more or atleast all of the following features: residue corresponding to X40 is aconstrained or basic residue, particularly arginine; residuecorresponding to X147 is an aromatic, non-polar or aliphatic residue,particularly methionine or leucine. In some embodiments, theketoreductase polypeptide can have in addition to the foregoingfeatures, one or more of the following features: residue correspondingto X96 is a polar, aromatic, non-polar, or aliphatic residueparticularly phenylalanine or valine; residue corresponding to X195 is anon-polar or aliphatic residue, particularly valine; residuecorresponding to X196 is a non-polar or aliphatic residue, particularlyleucine; residue corresponding to X226 is a non-polar or aliphaticresidue, particularly valine; residue corresponding to X248 is anon-polar or basic residue, particularly arginine or lysine; and residuecorresponding to X249 is an aromatic residue, particularly tryptophan.In some embodiments, the ketoreductase polypeptide can have in additionto the foregoing features, one or more of the following features:residue corresponding to X2 is a polar, non-polar, or aliphatic residue,particularly alanine; residue corresponding to X4 is a basic residue orcysteine, particularly cysteine; residue corresponding to X11 is anon-polar, aliphatic, or aromatic residue, particularly phenylalanine;residue corresponding to X80 is a non-polar, aliphatic, or polarresidue, particularly threonine; residue corresponding to X86 is anon-polar, aliphatic, or polar residue, particularly isoleucine; residuecorresponding to X105 is a non-polar, aliphatic, basic or acidicresidue, particularly glycine; residue corresponding to X129 is anon-polar or polar residue, particularly threonine; residuecorresponding to X153 is a polar, non-polar or aliphatic residue,particularly alanine; residue corresponding to X190 is an aromatic orconstrained residue, particularly histidine or proline; and residuecorresponding to X206 is a non-polar or aromatic residue, particularlyphenylalanine. As will be apparent to the skilled artisan, variouscombinations of the features in the foregoing can be used to form theketoreductases of the disclosure.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, can have additionally one or more or atleast all of the following features: residue corresponding to X40 is aconstrained or basic residue, particularly arginine; and residuecorresponding to X147 is an aromatic, non-polar or aliphatic residue,particularly methionine or leucine. In some embodiments, theketoreductase polypeptides can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20,1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residue differences at otheramino acid residue positions as compared to the reference sequence ofSEQ ID NO:2, 4 or 86. In some embodiments, the number of differences canbe 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24,26, 30, 35 or about 40 residue differences at other amino acid residues.In some embodiments, the differences comprise conservative mutations. Insome embodiments, the ketoreductase polypeptide comprises an amino acidsequence that is at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identical to a reference sequence basedon SEQ ID NO: 2, 4 or 86 having the preceding features, with the provisothat the ketoreductase has an amino acid sequence having at least thepreceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 can have additionally one or more or at least all of thefollowing features: residue corresponding to X96 is a polar, aromatic,non-polar, or aliphatic residue, particularly valine or phenylalanine;and residue corresponding to X147 is an aromatic, non-polar or aliphaticresidue, particularly methionine or leucine. In some embodiments, theketoreductase polypeptides can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20,1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residue differences at otheramino acid residue positions as compared to the reference sequence ofSEQ ID NO:2, 4 or 86. In some embodiments, the number of differences canbe 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24,26, 30, 35 or about 40 residue differences at other amino acid residues.In some embodiments, the differences comprise conservative mutations. Insome embodiments, the ketoreductase polypeptide comprises an amino acidsequence that is at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identical to a reference sequence basedon SEQ ID NO: 2, 4 or 86 having the preceding features, with the provisothat the ketoreductase has an amino acid sequence having at least thepreceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 can have additionally one or more or at least all of thefollowing features: residue corresponding to X40 is a constrained orbasic residue, particularly arginine; residue corresponding to X96 is apolar, aromatic, non-polar, or aliphatic residue, particularly valine orphenylalanine; and residue corresponding to X147 is an aromatic,non-polar or aliphatic residue, particularly methionine or leucine. Insome embodiments, the ketoreductase polypeptides can have additionally1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15,1-16, 1-18, 1-20, 1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residuedifferences at other amino acid residue positions as compared to thereference sequence of SEQ ID NO:2, 4 or 86. In some embodiments, thenumber of differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14,15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40 residue differences atother amino acid residues. In some embodiments, the differences compriseconservative mutations. In some embodiments, the ketoreductasepolypeptide comprises an amino acid sequence that is at least 85%, 86%,87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%identical to a reference sequence based on SEQ ID NO: 2, 4 or 86 havingthe preceding features, with the proviso that the ketoreductase has anamino acid sequence having at least the preceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 can have additionally one or more or at least all of thefollowing features: residue corresponding to X96 is a polar, aromatic,non-polar, or aliphatic residue, particularly valine or phenylalanine;residue corresponding to X147 is an aromatic, non-polar or aliphaticresidue, particularly methionine or leucine; residue corresponding toX195 is a non-polar or aliphatic residue, particularly valine; andresidue corresponding to X196 is a non-polar or aliphatic residue,particularly leucine. In some embodiments, the ketoreductasepolypeptides can have additionally 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8,1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20, 1-22, 1-24, 1- 26,1-30, 1-35 or about 1-40 residue differences at other amino acid residuepositions as compared to the reference sequence of SEQ ID NO:2, 4 or 86.In some embodiments, the number of differences can be 1, 2, 3, 4, 5, 6,7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40residue differences at other amino acid residues. In some embodiments,the differences comprise conservative mutations. In some embodiments,the ketoreductase polypeptide comprises an amino acid sequence that isat least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%,97%, 98%, or 99% identical to a reference sequence based on SEQ ID NO:2, 4 or 86 having the preceding features, with the proviso that theketoreductase has an amino acid sequence having at least the precedingfeatures.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X2 is a polar, non-polar,or aliphatic residue, particularly alanine. In some embodiments, theketoreductase polypeptides can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20,1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residue differences at otheramino acid residue positions as compared to the reference sequence ofSEQ ID NO:2, 4 or 86. In some embodiments, the number of differences canbe 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24,26, 30, 35 or about 40 residue differences at other amino acid residues.In some embodiments, the differences comprise conservative mutations. Insome embodiments, the ketoreductase polypeptide comprises an amino acidsequence that is at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identical to a reference sequence basedon SEQ ID NO: 2, 4 or 86 having the preceding features, with the provisothat the ketoreductase has an amino acid sequence having at least thepreceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X4 is cysteine or a basicresidue, particularly cysteine. In some embodiments, the ketoreductasepolypeptides can have additionally 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8,1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20, 1-22, 1-24, 1-26,1-30, 1-35 or about 1-40 residue differences at other amino acidresidues positions as compared to the reference sequence of SEQ ID NO:2,4 or 86. In some embodiments, the number of differences can be 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24, 26, 30, 35 orabout 40 residue differences at other amino acid residues. In someembodiments, the differences comprise conservative mutations. In someembodiments, the ketoreductase polypeptide comprises an amino acidsequence that is at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identical to a reference sequence basedon SEQ ID NO: 2, 4 or 86 having the preceding features, with the provisothat the ketoreductase has an amino acid sequence having at least thepreceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X11 is a non-polar,aliphatic, or aromatic residue, particularly phenylalanine. In someembodiments, the ketoreductase polypeptides can have additionally 1-2,1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16,1-18, 1-20, 1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residuedifferences at other amino acid residue positions as compared to thereference sequence of SEQ ID NO:2, 4 or 86. In some embodiments, thenumber of differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14,15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40 residue differences atother amino acid residues. In some embodiments, the differences compriseconservative mutations. In some embodiments, the ketoreductasepolypeptide comprises an amino acid sequence that is at least 85%, 86%,87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%identical to a reference sequence based on SEQ ID NO: 2, 4 or 86 havingthe preceding features, with the proviso that the ketoreductase has anamino acid sequence having at least the preceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X40 is a constrained orbasic residue, particularly arginine. In some embodiments, theketoreductase polypeptides can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20,1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residue differences at otheramino acid residue positions as compared to the reference sequence ofSEQ ID NO:2, 4 or 86. In some embodiments, the number of differences canbe 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24,26, 30, 35 or about 40 residue differences at other amino acid residues.In some embodiments, the differences comprise conservative mutations. Insome embodiments, the ketoreductase polypeptide comprises an amino acidsequence that is at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identical to a reference sequence basedon SEQ ID NO: 2, 4 or 86 having the preceding features, with the provisothat the ketoreductase has an amino acid sequence having at least thepreceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X80 is a non-polar,aliphatic, or polar residue, particularly threonine. In someembodiments, the ketoreductase polypeptides can have additionally 1-2,1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16,1-18, 1-20, 1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residuedifferences at other amino acid residue positions as compared to thereference sequence of SEQ ID NO:2, 4 or 86. In some embodiments, thenumber of differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14,15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40 residue differences atother amino acid residues. In some embodiments, the differences compriseconservative mutations. In some embodiments, the ketoreductasepolypeptide comprises an amino acid sequence that is at least 85%, 86%,87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%identical to a reference sequence based on SEQ ID NO: 2, 4 or 86 havingthe preceding features, with the proviso that the ketoreductase has anamino acid sequence having at least the preceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X86 is a non-polar,aliphatic, or polar residue, particularly isoleucine. In someembodiments, the ketoreductase polypeptides can have additionally 1-2,1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16,1-18, 1-20, 1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residuedifferences at other amino acid residue positions as compared to thereference sequence of SEQ ID NO:2, 4 or 86. In some embodiments, thenumber of differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14,15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40 residue differences atother amino acid residues. In some embodiments, the differences compriseconservative mutations. In some embodiments, the ketoreductasepolypeptide comprises an amino acid sequence that is at least 85%, 86%,87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%identical to a reference sequence based on SEQ ID NO: 2, 4 or 86 havingthe preceding features, with the proviso that the ketoreductase has anamino acid sequence having at least the preceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X96 is a polar, aromatic,non-polar, or aliphatic residue, particularly phenylalanine or valine.In some embodiments, the ketoreductase polypeptides can haveadditionally 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12,1-14, 1-15, 1-16, 1-18, 1-20, 1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40residue differences at other amino acid residue positions as compared tothe reference sequence of SEQ ID NO:2, 4 or 86. In some embodiments, thenumber of differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14,15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40 residue differences atother amino acid residues. In some embodiments, the differences compriseconservative mutations. In some embodiments, the ketoreductasepolypeptide comprises an amino acid sequence that is at least 85%, 86%,87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%identical to a reference sequence based on SEQ ID NO: 2, 4 or 86 havingthe preceding features, with the proviso that the ketoreductase has anamino acid sequence having at least the preceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X105 is a non-polar,aliphatic, basic or acidic residue, particularly glycine. In someembodiments, the ketoreductase polypeptides can have additionally 1-2,1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16,1-18, 1-20, 1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residuedifferences at other amino acid residue positions as compared to thereference sequence of SEQ ID NO:2, 4 or 86. In some embodiments, thenumber of differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14,15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40 residue differences atother amino acid residues. In some embodiments, the differences compriseconservative mutations. In some embodiments, the ketoreductasepolypeptide comprises an amino acid sequence that is at least 85%, 86%,87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%identical to a reference sequence based on SEQ ID NO: 2, 4 or 86 havingthe preceding features, with the proviso that the ketoreductase has anamino acid sequence having at least the preceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X129 is a non-polar orpolar residue, particularly threonine. In some embodiments, theketoreductase polypeptides can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20,1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residue differences at otheramino acid residue positions as compared to the reference sequence ofSEQ ID NO:2, 4 or 86. In some embodiments, the number of differences canbe 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24,26, 30, 35 or about 40 residue differences at other amino acid residues.In some embodiments, the differences comprise conservative mutations. Insome embodiments, the ketoreductase polypeptide comprises an amino acidsequence that is at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identical to a reference sequence basedon SEQ ID NO: 2, 4 or 86 having the preceding features, with the provisothat the ketoreductase has an amino acid sequence having at least thepreceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X147 s an aromatic,non-polar or aliphatic residue, particularly methionine or leucine. Insome embodiments, the ketoreductase polypeptides can have additionally1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15,1-16, 1-18, 1-20, 1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residuedifferences at other amino acid residue positions as compared to thereference sequence of SEQ ID NO:2, 4 or 86. In some embodiments, thenumber of differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14,15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40 residue differences atother amino acid residues. In some embodiments, the differences compriseconservative mutations. In some embodiments, the ketoreductasepolypeptide comprises an amino acid sequence that is at least 85%, 86%,87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%identical to a reference sequence based on SEQ ID NO: 2, 4 or 86 havingthe preceding features, with the proviso that the ketoreductase has anamino acid sequence having at least the preceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X153 s a polar, non-polaror aliphatic residue, particularly alanine or serine. In someembodiments, the ketoreductase polypeptides can have additionally 1-2,1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16,1-18, 1-20, 1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residuedifferences at other amino acid residue positions as compared to thereference sequence of SEQ ID NO:2, 4 or 86. In some embodiments, thenumber of differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14,15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40 residue differences atother amino acid residue positions. In some embodiments, the differencescomprise conservative mutations. In some embodiments, the ketoreductasepolypeptide comprises an amino acid sequence that is at least 85%, 86%,87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%identical to a reference sequence based on SEQ ID NO: 2, 4 or 86 havingthe preceding features, with the proviso that the ketoreductase has anamino acid sequence having at least the preceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X190 is an aromatic orconstrained residue, particularly histidine or proline. In someembodiments, the ketoreductase polypeptides can have additionally 1-2,1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16,1-18, 1-20, 1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residuedifferences at other amino acid residue positions as compared to thereference sequence of SEQ ID NO:2, 4 or 86. In some embodiments, thenumber of differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14,15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40 residue differences atother amino acid residues. In some embodiments, the differences compriseconservative mutations. In some embodiments, the ketoreductasepolypeptide comprises an amino acid sequence that is at least 85%, 86%,87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%identical to a reference sequence based on SEQ ID NO: 2, 4 or 86 havingthe preceding features, with the proviso that the ketoreductase has anamino acid sequence having at least the preceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X195 is a non-polar oraliphatic residue, particularly valine. In some embodiments, theketoreductase polypeptides can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20,1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residue differences at otheramino acid residue positions as compared to the reference sequence ofSEQ ID NO:2, 4 or 86. In some embodiments, the number of differences canbe 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24,26, 30, 35 or about 40 residue differences at other amino acid residues.In some embodiments, the differences comprise conservative mutations. Insome embodiments, the ketoreductase polypeptide comprises an amino acidsequence that is at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identical to a reference sequence basedon SEQ ID NO: 2, 4 or 86 having the preceding features, with the provisothat the ketoreductase has an amino acid sequence having at least thepreceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X196 is a non-polar oraliphatic residue, particularly leucine. In some embodiments, theketoreductase polypeptides can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20,1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residue differences at otheramino acid residue positions as compared to the reference sequence ofSEQ ID NO:2, 4 or 86. In some embodiments, the number of differences canbe 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24,26, 30, 35 or about 40 residue differences at other amino acid residues.In some embodiments, the differences comprise conservative mutations. Insome embodiments, the ketoreductase polypeptide comprises an amino acidsequence that is at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identical to a reference sequence basedon SEQ ID NO: 2, 4 or 86 having the preceding features, with the provisothat the ketoreductase has an amino acid sequence having at least thepreceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X206 is a non-polar oraromatic residue, particularly phenylalanine. In some embodiments, theketoreductase polypeptides can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20,1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residue differences at otheramino acid residue positions as compared to the reference sequence ofSEQ ID NO:2, 4 or 86. In some embodiments, the number of differences canbe 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24,26, 30, 35 or about 40 residue differences at other amino acid residues.In some embodiments, the differences comprise conservative mutations. Insome embodiments, the ketoreductase polypeptide comprises an amino acidsequence that is at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identical to a reference sequence basedon SEQ ID NO: 2, 4 or 86 having the preceding features, with the provisothat the ketoreductase has an amino acid sequence having at least thepreceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X226 is a non-polar oraliphatic residue, particularly valine. In some embodiments, theketoreductase polypeptides can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20,1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residue differences at otheramino acid residue positions as compared to the reference sequence ofSEQ ID NO:2, 4 or 86. In some embodiments, the number of differences canbe 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24,26, 30, 35 or about 40 residue differences at other amino acid residues.In some embodiments, the differences comprise conservative mutations. Insome embodiments, the ketoreductase polypeptide comprises an amino acidsequence that is at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identical to a reference sequence basedon SEQ ID NO: 2, 4 or 86 having the preceding features, with the provisothat the ketoreductase has an amino acid sequence having at least thepreceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X248 is a non-polar orbasic residue, particularly lysine or arginine. In some embodiments, theketoreductase polypeptides can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20,1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residue differences at otheramino acid residue positions as compared to the reference sequence ofSEQ ID NO:2, 4 or 86. In some embodiments, the number of differences canbe 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24,26, 30, 35 or about 40 residue differences at other amino acid residues.In some embodiments, the differences comprise conservative mutations. Insome embodiments, the ketoreductase polypeptide comprises an amino acidsequence that is at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identical to a reference sequence basedon SEQ ID NO: 2, 4 or 86 having the preceding features, with the provisothat the ketoreductase has an amino acid sequence having at least thepreceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, further includes at least the followingadditional feature: residue corresponding to X249 is an aromaticresidue, particularly tryptophan. In some embodiments, the ketoreductasepolypeptides can have additionally 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8,1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20, 1-22, 1-24, 1- 26,1-30, 1-35 or about 1-40 residue differences at other amino acid residuepositions as compared to the reference sequence of SEQ ID NO:2, 4 or 86.In some embodiments, the number of differences can be 1, 2, 3, 4, 5, 6,7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40residue differences at other amino acid residues. In some embodiments,the differences comprise conservative mutations. In some embodiments,the ketoreductase polypeptide comprises an amino acid sequence that isat least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%,97%, 98%, or 99% identical to a reference sequence based on SEQ ID NO:2, 4 or 86 having the preceding features, with the proviso that theketoreductase has an amino acid sequence having at least the precedingfeatures.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresfor the various combinations of the residues corresponding to X94, X199and X202 as described herein, can have additionally one or more or atleast all of the following features: residue corresponding to X40 is aconstrained or basic residue, particularly arginine; residue and residuecorresponding to X147 is an aromatic, non-polar or aliphatic residue,particularly methionine or leucine. In some embodiments, theketoreductase polypeptide can have in addition to the foregoingfeatures, one or more of the following features: residue correspondingto X96 is a polar, aromatic, non-polar, or aliphatic residueparticularly valine; residue corresponding to X195 is a non-polar oraliphatic residue, particularly valine; residue corresponding to X196 isa non-polar or aliphatic residue, particularly leucine; residuecorresponding to X226 is a non-polar or aliphatic residue, particularlyvaline; residue corresponding to X248 is a non-polar or basic residue,particularly arginine or lysine; and residue corresponding to X249 is anaromatic residue, particularly tryptophan. In some embodiments, theketoreductase polypeptide can have in addition to the foregoingfeatures, one or more of the following features: residue correspondingto X2 is a polar, non-polar, or aliphatic residue; residue correspondingto X4 is a basic residue or cysteine; residue corresponding to X11 is anon-polar, aliphatic, or aromatic residue; residue corresponding to X80is a non-polar, aliphatic, or polar residue; residue corresponding toX86 is a non-polar, aliphatic, or polar residue; residue correspondingto X105 is a non-polar, aliphatic, basic or acidic residue; residuecorresponding to X129 is a non-polar or polar residue; residuecorresponding to X153 is a polar, non-polar or aliphatic residue;residue corresponding to X190 is an aromatic or constrained residue; andresidue corresponding to X206 is a non-polar or aromatic residue. Aswill be apparent to the skilled artisan, various combinations of thefeatures in the foregoing can be used to form the ketoreductases of thedisclosure.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresat residue corresponding to X202 as described herein (i.e., valine orleucine), further includes at least the following additional feature:residue corresponding to X153 is a polar, non-polar or aliphaticresidue, particularly alanine or serine. In some embodiments, theketoreductase polypeptides can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20,1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residue differences at otheramino acid residue positions as compared to the reference sequence basedon SEQ ID NO:2, 4 or 86 having the preceding features (e.g., SEQ IDNO:46, 52 or 54). In some embodiments, the number of differences can be1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24, 26,30, 35 or about 40 residue differences at other amino acid residues. Insome embodiments, the ketoreductase polypeptide comprises an amino acidsequence that is at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identical to a reference sequence basedon SEQ ID NO:2, 4 or 86 having the preceding features (e.g., SEQ IDNO:46, 52 or 54), with the proviso that the ketoreductase has an aminoacid sequence having at least the preceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresat residue corresponding to X202 as described herein, further includesat least the following additional feature: residue corresponding to X147is an aromatic, non-polar or aliphatic residue, particularly methionine.In some embodiments, the ketoreductase polypeptides can haveadditionally 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12,1-14, 1-15, 1-16, 1-18, 1-20, 1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40residue differences at other amino acid residue positions as compared tothe reference sequence of SEQ ID NO:2, 4 or 86 having the precedingfeatures (e.g., SEQ ID NO:44). In some embodiments, the number ofdifferences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16,18, 20, 22, 24, 26, 30, 35 or about 40 residue differences at otheramino acid residues. In some embodiments, the ketoreductase polypeptidecomprises an amino acid sequence that is at least 85%, 86%, 87%, 88%,89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identical to areference sequence based on SEQ ID NO:2, 4 or 86 having the precedingfeatures (e.g., SEQ ID NO:44), with the proviso that the ketoreductaseamino acid sequence has at least the preceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresat residue corresponding to X202 as described herein, further includesat least the following additional features: residue corresponding to X80is a non-polar, aliphatic, or polar residue, particularly threonine; andresidue corresponding to X153 is a polar, non-polar or aliphaticresidue, particularly alanine or serine. In some embodiments, theketoreductase polypeptides can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20,1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residue differences at otheramino acid residue positions as compared to the reference sequence ofSEQ ID NO:2, 4 or 86 having the preceding features (e.g., SEQ ID NO:18).In some embodiments, the number of differences can be 1, 2, 3, 4, 5, 6,7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40residue differences at other amino acid residues. In some embodiments,the ketoreductase polypeptide comprises an amino acid sequence that isat least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%,97%, 98%, or 99% identical to a reference sequence based on SEQ ID NO:2,4 or 86 having the preceding features (e.g., SEQ ID NO:18), with theproviso that the ketoreductase amino acid sequence has at least thepreceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresat residues corresponding to X94 and X202 as described herein, furtherincludes at least the following additional features: residuecorresponding to X96 is a polar, aromatic, non-polar, or aliphaticresidue, particularly phenylalanine. In some embodiments, theketoreductase polypeptides can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20,1-22, 1-24, 1- 26, 1-30, 1-35 or about 1-40 residue differences at otheramino acid residue positions as compared to the reference sequence ofSEQ ID NO:2, 4 or 86 having the preceding features (e.g., SEQ ID NO:16).In some embodiments, the number of differences can be 1, 2, 3, 4, 5, 6,7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40residue differences at other amino acid residues. In some embodiments,the ketoreductase polypeptide comprises an amino acid sequence that isat least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%,97%, 98%, or 99% identical to a reference sequence based on SEQ ID NO:2,4 or 86 having the preceding features (e.g., SEQ ID NO:16), with theproviso that the ketoreductase amino acid sequence has at least thepreceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresat residues corresponding to X199 and X202 as described herein, furtherincludes at least the following additional feature: residuecorresponding to X153 is a polar, non-polar or aliphatic residue,particularly alanine or serine. In some embodiments, the ketoreductasepolypeptides can have additionally 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8,1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20, 1-22, 1-24, 1-26,1-30, 1- 35 or about 1-40 residue differences at other amino acidresidue positions as compared to the reference sequence of SEQ ID NO:2,4 or 86 having the preceding features (e.g., SEQ ID NO:42, 50, 56). Insome embodiments, the number of differences can be 1, 2, 3, 4, 5, 6, 7,8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40residue differences at other amino acid residues. In some embodiments,the ketoreductase polypeptide comprises an amino acid sequence that isat least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%,97%, 98%, or 99% identical to a reference sequence based on SEQ ID NO:2,4 or 86 having the preceding features (e.g., SEQ ID NO:42, 50, 56), withthe proviso that the ketoreductase amino acid sequence has at least thepreceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresat residues corresponding to X94, X199 and X202 as described herein,further includes at least the following additional features: residuecorresponding to X40 is a constrained or basic residue, particularlyarginine. In some embodiments, the ketoreductase polypeptides can haveadditionally 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12,1-14, 1-15, 1-16, 1-18, 1-20, 1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40residue differences at other amino acid residue positions as compared tothe reference sequence of SEQ ID NO:2, 4 or 86 having the precedingfeatures (e.g., SEQ ID NO:12). In some embodiments, the number ofdifferences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16,18, 20, 22, 24, 26, 30, 35 or about 40 residue differences at otheramino acid residues. In some embodiments, the ketoreductase polypeptidecomprises an amino acid sequence that is at least 85%, 86%, 87%, 88%,89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identical to areference sequence based on SEQ ID NO:2, 4 or 86 having the precedingfeatures (e.g., SEQ ID NO:12), with the proviso that the ketoreductaseamino acid sequence has at least the preceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresat residues corresponding to X94, X199 and X202 as described herein,further includes at least the following additional features: residuecorresponding to X147 is an aromatic, non-polar or aliphatic residue,particularly methionine or leucine. In some embodiments, theketoreductase polypeptides can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20,1-22, 1-24, 1- 26, 1-30, 1-35 or about 1-40 residue differences at otheramino acid residue positions as compared to the reference sequence ofSEQ ID NO:2, 4 or 86 having the preceding features (e.g., SEQ ID NO:6).In some embodiments, the number of differences can be 1, 2, 3, 4, 5, 6,7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40residue differences at other amino acid residues. In some embodiments,the ketoreductase polypeptide comprises an amino acid sequence that isat least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%,97%, 98%, or 99% identical to a reference sequence based on SEQ ID NO:2,4 or 86 having the preceding features (e.g., SEQ ID NO:6), with theproviso that the ketoreductase amino acid sequence has at least thepreceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresat residues corresponding to X94, X199 and X202 as described herein,further includes at least the following additional features: residuecorresponding to X153 is a polar, non-polar or aliphatic residue,particularly alanine or serine. In some embodiments, the ketoreductasepolypeptides can have additionally 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8,1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20, 1-22, 1-24, 1- 26,1-30, 1-35 or about 1-40 residue differences at other amino acid residuepositions as compared to the reference sequence of SEQ ID NO:2, 4 or 86having the preceding features (e.g., SEQ ID NO: 34 or 36). In someembodiments, the number of differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 14, 15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40 residuedifferences at other amino acid residues. In some embodiments, theketoreductase polypeptide comprises an amino acid sequence that is atleast 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%,98%, or 99% identical to a reference sequence based on SEQ ID NO:2, 4 or86 having the preceding features (e.g., SEQ ID NO: 34 or 36), with theproviso that the ketoreductase amino acid sequence has at least thepreceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresat residues corresponding to X94, X199 and X202 as described herein,further includes at least the following additional features: residuecorresponding to X40 is a constrained or basic residue, particularlyarginine; and residue corresponding to X147 is an aromatic, non-polar oraliphatic residue, particularly methionine or leucine. In someembodiments, the ketoreductase polypeptides can have additionally 1-2,1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16,1-18, 1-20, 1-22, 1-24, 1- 26, 1-30, 1-35 or about 1-40 residuedifferences at other amino acid residue positions as compared to thereference sequence of SEQ ID NO:2, 4 or 86 having the preceding features(e.g., SEQ ID NO:10). In some embodiments, the number of differences canbe 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24,26, 30, 35 or about 40 residue differences at other amino acid residues.In some embodiments, the ketoreductase polypeptide comprises an aminoacid sequence that is at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%,93%, 94%, 95%, 96%, 97%, 98%, or 99% identical to a reference sequencebased on SEQ ID NO:2, 4 or 86 having the preceding features (e.g., SEQID NO:10), with the proviso that the ketoreductase amino acid sequencehas at least the preceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresat residues corresponding to X94, X199 and X202 as described herein,further includes at least the following additional features: residuecorresponding to X105 is a non-polar, aliphatic, basic or acidicresidue, particularly glycine; residue corresponding to X153 is a polar,non-polar or aliphatic residue, particularly alanine; and residuecorresponding to X206 is a non-polar or aromatic residue, particularlyphenylalanine. In some embodiments, the ketoreductase polypeptides canhave additionally 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11,1-12, 1-14, 1-15, 1-16, 1-18, 1-20, 1-22, 1-24, 1-26, 1-30, 1-35 orabout 1-40 residue differences at other amino acid residue positions ascompared to the reference sequence of SEQ ID NO:2, 4 or 86 having thepreceding features (e.g., SEQ ID NO:38). In some embodiments, the numberof differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16,18, 20, 22, 24, 26, 30, 35 or about 40 residue differences at otheramino acid residues. In some embodiments, the ketoreductase polypeptidecomprises an amino acid sequence that is at least 85%, 86%, 87%, 88%,89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identical to areference sequence based on SEQ ID NO:2, 4 or 86 having the precedingfeatures (e.g., SEQ ID NO:38), with the proviso that the ketoreductaseamino acid sequence has at least the preceding features.

In some embodiments, an improved ketoreductase comprising an amino acidsequence based on the sequence formula of SEQ ID NO:83, 84 or 87, or aregion thereof, such as residues 90-211, having the specified featuresat residues corresponding to X94, X199 and X202 as described herein,further includes at least the following additional features: residuecorresponding to X96 is a polar, aromatic, non-polar, or aliphaticresidue, particularly serine, valine, or phenylalanine; residuecorresponding to X129 is a non-polar or polar residue, particularlythreonine; and residue corresponding to X206 is a non-polar or aromaticresidue, particularly phenylalanine. In some embodiments, theketoreductase polypeptides can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20,1-22, 1-24, 1-26, 1-30, 1-35 or about 1-40 residue differences at otheramino acid residues as compared to the reference sequence of SEQ IDNO:2, 4 or 86 having the preceding features (e.g., SEQ ID NO:40). Insome embodiments, the number of differences can be 1, 2, 3, 4, 5, 6, 7,8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40residue differences at other amino acid residues. In some embodiments,the ketoreductase polypeptide comprises an amino acid sequence that isat least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%,97%, 98%, or 99% identical to a reference sequence based on SEQ ID NO:2,4 or 86 having the preceding features (e.g., SEQ ID NO:40), with theproviso that the ketoreductase amino acid sequence has at least thepreceding features.

In some embodiments, the improved ketoreductases of the disclosurecomprises an amino acid sequence that has a region or domaincorresponding to residues 90-211 of the sequence formula of SEQ IDNO:83, 84 or 87 in which the residue corresponding to X202 is valine orleucine. In some embodiments, the region or domain corresponding toresidues 90-211 can have additionally 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8,1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, or 1-20 residuedifferences at other amino acid residue positions as compared to thecorresponding domain of a reference sequence based on SEQ ID NO: 2, 4 or86. In some embodiments, the number of differences can be 1, 2, 3, 4, 5,6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, or about 20 residue differences.In some embodiments, the differences comprise conservative mutations. Insome embodiments, the ketoreductase polypeptide comprises an amino acidsequence with a domain or region that is at least 85%, 86%, 87%, 88%,89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identical tothe domain or region corresponding to residue 90-211 of a referencesequence based on SEQ ID NO: 2, 4 or 86 having the preceding features atresidue corresponding to X202, with the proviso that the ketoreductasedomain or region comprises an amino acid sequence having at least thepreceding feature.

In some embodiments, the improved ketoreductases of the disclosurecomprises an amino acid sequence that has a region or domaincorresponding to residues 90-211 of the sequence formula of SEQ IDNO:83, 84 or 87 in which the region or domain has the followingfeatures: residue corresponding to X94 is an aliphatic or polar residue,particularly alanine or threonine; and residue corresponding to X202 isa valine or leucine. In some embodiments, the ketoreductase has an aminoacid sequence in which the residue corresponding to X94 is a polarresidue, and the residue corresponding to X202 is valine or leucine. Insome embodiments, the ketoreductase has an amino acid sequence in whichthe residue corresponding to X94 is threonine, and the residuecorresponding to X202 is valine or leucine. In some embodiments, theregion or domain corresponding to residues 90-211 can have additionally1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15,1-16, 1-18, or 1-20 residue differences at other amino acid residuepositions as compared to the corresponding domain of a referencesequence based on SEQ ID NO: 2, 4 or 86. In some embodiments, the numberof differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16,18, or about 20 residue differences. In some embodiments, thedifferences comprise conservative mutations. In some embodiments, theketoreductase polypeptide comprises an amino acid sequence with a domainor region that is at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identical to the domain or regioncorresponding to residues 90-211 of a reference sequence based on SEQ IDNO: 2, 4 or 86 having the preceding features, with the proviso that theketoreductase domain or region comprises an amino acid sequence havingat least the preceding features.

In some embodiments, the improved ketoreductases of the disclosurecomprises an amino acid sequence that has a region or domaincorresponding to residues 90-211 of the sequence formula of SEQ IDNO:83, 84 or 87 having the following features: residue corresponding toX94 is an aliphatic or polar residue, particularly alanine or threonine;residue corresponding to X199 is an aliphatic, constrained or polarresidue, particularly alanine, asparagine, or histidine; and residuecorresponding to X202 is a valine or leucine. In some embodiments, theresidue corresponding to X94 is a polar residue; the residuecorresponding to X199 is an aliphatic, constrained, or polar residue;and the residue corresponding to X202 is valine or leucine. In someembodiments, the ketoreductase has an amino acid sequence in which theresidue corresponding to X94 is threonine; residue corresponding to X199is alanine, asparagine, or histidine; and the residue corresponding toX202 is valine or leucine. In some embodiments, the region or domaincorresponding to residues 90-211 can have additionally 1-2, 1-3, 1-4,1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, or1-20 residue differences at other amino acid residue positions ascompared to the corresponding domain of a reference sequence based onSEQ ID NO: 2, 4 or 86. In some embodiments, the number of differencescan be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, or about20 residue differences. In some embodiments, the differences compriseconservative mutations. In some embodiments, the ketoreductasepolypeptide comprises an amino acid sequence with a domain or regionthat is at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%,96%, 97%, 98%, or 99% identical to the domain or region corresponding toresidues 90-211 of a reference sequence based on SEQ ID NO: 2, 4 or 86having the preceding features, with the proviso that the ketoreductasedomain or region comprises an amino acid sequence having at least thepreceding features.

In some embodiments, the ketoreductase polypeptide with a domain orregion corresponding to residues 90-211 of the sequence formula of SEQID NO:83, 84 or 87 and having the specified features for the variouscombination of residues corresponding to residues X94, X199, and X202 asdescribed herein, can further include in the region or domain one ormore of the features selected from the following: residue correspondingto X96 is a polar, aromatic, non-polar, or aliphatic residue; residuecorresponding to X105 is a non-polar, aliphatic, basic or acidicresidue; residue corresponding to X129 is a non-polar or polar residue;residue corresponding to X147 is an aromatic, non-polar or aliphaticresidue; residue corresponding to X153 is a polar, non-polar oraliphatic residue; residue corresponding to X190 is an aromatic orconstrained residue; residue corresponding to X195 is a non-polar oraliphatic residue; residue corresponding to X196 is a non-polar oraliphatic residue; and residue corresponding to X206 is a non-polar oraromatic residue. In some embodiments, the region or domaincorresponding to residues 90-211 can have additionally from about 1-2,1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16,1-18, or 1-20 residue differences at other amino acid residues notspecified by X above as compared to the corresponding domain of areference sequence based on SEQ ID NO: 2, 4 or 86. In some embodiments,the number of differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,14, 15, 16, 18, or about 20 residue differences at other amino acidresidues in the domain. In some embodiments, the differences compriseconservative mutations.

In some embodiments, the ketoreductases polypeptides having a domain orregion with an amino acid sequence corresponding to residues 90-211 ofthe sequence formula of SEQ ID NO:83, 84 or 87, as described above, canhave one or more conservative mutations in the domain or region ascompared to the amino acid sequence of the corresponding domain of SEQID NO: 2, 4 or 86. Examples of such conservative mutations include aminoacid replacements such as, but limited to: replacement of residuecorresponding to X145 glutamic acid (E) with another acidic residue,e.g., aspartic acid; replacement of residue corresponding to X153leucine (L) with another aliphatic residue, e.g., alanine; replacementof residue corresponding to X195 leucine (L) with another aliphaticresidue, e.g., valine; and replacement of residue corresponding to X196with another aliphatic residue, e.g., leucine.

In some embodiments, the ketoreductase polypeptide with a domain orregion corresponding to residues 90-211 of the sequence formula of SEQID NO:83, 84 or 87 and having the specified features for the variouscombination of residues corresponding to residues X94, X199, and X202 asdescribed herein, can further include in the region or domain one ormore of the features selected from the following: residue correspondingto X96 is serine, threonine, glutamine, asparagine, glycine, methionine,alanine, valine, leucine, isoleucine, tyrosine, phenylalanine, ortryptophan, particularly asparagine, serine, valine, or phenylalanine;residue corresponding to X105 is glycine, methionine, alanine, valine,leucine, isoleucine, arginine, lysine, aspartic acid, or glutamic acid,particularly glutamic acid, lysine, alanine, or glycine; residuecorresponding to X129 is glycine, methionine, alanine, valine, leucine,isoleucine, serine, threonine, glutamine, or asparagine, particularlymethionine or threonine; residue corresponding to X147 is tyrosine,phenylalanine, tryptophan, glycine, methionine, alanine, valine,leucine, or isoleucine, particularly phenylalanine, methionine, orleucine; residue corresponding to X153 is a serine, threonine,glutamine, asparagine, glycine, methionine, alanine, valine, leucine, orisoleucine, particularly leucine, alanine, or serine; residuecorresponding to X190 is tyrosine, phenylalanine, tryptophan, histidine,or proline, particularly tyrosine, histidine or proline; residuecorresponding to X195 is glycine, methionine, alanine, valine, leucine,or isoleucine, particularly leucine or valine; residue corresponding toX196 is glycine, methionine, alanine, valine, leucine, or isoleucine,particularly leucine; residue corresponding to X206 is glycine,methionine, alanine, valine, leucine, isoleucine, tyrosine,phenylalanine, or tryptophan, particularly methionine or phenylalanine.In some embodiments, the region or domain corresponding to residues90-211 can have additionally from about 1-2, 1-3, 1-4, 1-5, 1-6, 1-7,1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, or 1-20 residuedifferences at other amino acid residue positions not specified by Xabove as compared to the corresponding domain of a reference sequencebased on SEQ ID NO: 2, 4 or 86. In some embodiments, the number ofdifferences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16,18, or about 20 residue differences at other amino acid residues in thedomain. In some embodiments, the differences comprise conservativemutations.

In some embodiments, the ketoreductase polypeptide with a domain orregion corresponding to residues 90-211 of the sequence formula of SEQID NO:83, 84 or 87 and having the specified features for the variouscombination of residues corresponding to residues X94, X199, and X202 asdescribed herein, can further include in the region or domain thefollowing feature: residue corresponding to X147 is an aromatic,non-polar or aliphatic residue, particularly methionine or leucine. Insome embodiments, the region or domain corresponding to residues 90-211can have additionally 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10,1-11, 1-12, 1-14, 1-15, 1-16, 1-18, or 1-20 residue differences at otheramino acid residue positions as compared to the corresponding domain ofa reference sequence based on SEQ ID NO: 2, 4 or 86. In someembodiments, the number of differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 14, 15, 16, 18, or about 20 residue differences. In someembodiments, the differences comprise conservative mutations. In someembodiments, the ketoreductase polypeptide comprises an amino acidsequence with a domain or region that is at least 85%, 86%, 87%, 88%,89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identical tothe domain or region corresponding to residues 90-211 of a referencesequence based on SEQ ID NO: 2, 4 or 86 having the preceding features,with the proviso that the ketoreductase domain or region comprises anamino acid sequence having at least the preceding features.

In some embodiments, the ketoreductase polypeptide with a domain orregion corresponding to residues 90-211 of the sequence formula of SEQID NO:83, 84 or 87 and having the specified features for the variouscombination of residues corresponding to residues X94, X199, and X202 asdescribed herein, can further include in the region or domain thefollowing feature: residue corresponding to X96 is a polar, aromatic,non-polar, or aliphatic residue, particularly valine or phenylalanine;and residue corresponding to X147 is an aromatic, non-polar or aliphaticresidue, particularly methionine or leucine. In some embodiments, theregion or domain corresponding to residues 90-211 can have additionally1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15,1-16, 1-18, or 1-20 residue differences at other amino acid residuepositions as compared to the corresponding domain of a referencesequence based on SEQ ID NO: 2, 4 or 86. In some embodiments, the numberof differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16,18, or about 20 residue differences. In some embodiments, thedifferences comprise conservative mutations. In some embodiments, theketoreductase polypeptide comprises an amino acid sequence with a domainor region that is at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identical to the domain or regioncorresponding to residues 90-211 of a reference sequence based on SEQ IDNO: 2, 4 or 86 having the preceding features, with the proviso that theketoreductase domain or region comprises an amino acid sequence havingat least the preceding features.

In some embodiments, the ketoreductase polypeptide can further comprisea domain or region corresponding to residues 1-89 of the sequenceformula of SEQ ID NO:83, 84 or 87, where the domain or region can haveone or more of the following features: residue corresponding to X2 is apolar, non-polar, or aliphatic residue; residue corresponding to X4 is abasic residue or cysteine; residue corresponding to X11 is a non-polar,aliphatic, or aromatic residue; residue corresponding to X40 is aconstrained or basic residue; residue corresponding to X80 is anon-polar, aliphatic, or polar residue; and residue corresponding to X86is a non-polar, aliphatic, or polar residue. In some embodiments, thepolypeptides comprising a region or domain corresponding to residues1-89 of the sequence formula of SEQ ID NO:83, 84 or 87 can haveadditionally one or more residue differences at residue positions notspecified by X above as compared to the reference sequence of SEQ ID NO:2, 4 or 86. In some embodiments, the differences can be 1-2, 1-3, 1-4,1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, or 1-16 residuedifferences at other amino acid residue positions not defined by X aboveas compared to the reference sequence of SEQ ID NO: 2, 4 or 86. In someembodiments, the number of differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 14, 15, or 16 residue differences at other amino acidresidue positions. In some embodiments, the differences compriseconservative mutations.

In some embodiments, the ketoreductase polypeptide can further comprisea domain or region corresponding to residues 1-89 of the sequenceformula of SEQ ID NO:83, 84 or 87, where the domain or region can haveone or more of the following features: residue corresponding to X2 is aserine, threonine, glutamine, or asparagine, glycine, methionine,alanine, valine, leucine, or isoleucine, particularly serine, threonine,or alanine; residue corresponding to X4 is an arginine, or lysine, orcysteine, particularly arginine or cysteine; residue corresponding toX11 is a glycine, methionine, alanine, valine, leucine, isoleucine,tyrosine, phenylalanine, or tryptophan, particularly isoleucine,leucine, or phenylalanine; residue corresponding to X40 is proline,histidine, arginine, or lysine, particularly histidine or arginine;residue corresponding to X80 is glycine, methionine, alanine, valine,leucine, isoleucine, serine, threonine, glutamine, or asparagine,particularly alanine or threonine; and residue corresponding to X86 isserine, threonine, glutamine, asparagine, glycine, methionine, alanine,valine, leucine, or isoleucine, particularly threonine or isoleucine. Insome embodiments, the polypeptides comprising a region or domaincorresponding to residues 1-89 of the sequence formula of SEQ ID NO:83,84 or 87 can have additionally one or more residue differences atresidue positions not specified by X above as compared to the referencesequence of SEQ ID NO: 2, 4 or 86. In some embodiments, the differencescan be 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14,1-15, or 1-16 residue differences at other amino acid residue positionsnot defined by X above as compared to the reference sequence of SEQ IDNO: 2, 4 or 86. In some embodiments, the number of differences can be 1,2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, or 16 residue differences atother amino acid residue positions. In some embodiments, the differencescomprise conservative mutations.

In some embodiments, the ketoreductase polypeptide can further comprisea domain or region corresponding to residues 1-89 of the sequenceformula of SEQ ID NO:83, 84 or 87, where the domain or region can haveat least the following feature: residue corresponding to X40 is aconstrained or basic residue, particularly arginine. In someembodiments, the polypeptides comprising a region or domaincorresponding to residues 1-89 of the sequence formula of SEQ ID NO:111, 112, or 139 can have additionally one or more residue differencesat other residue positions as compared to the reference sequence of SEQID NO: 2, 4 or 114. In some embodiments, the region or domaincorresponding to residues 1-89 can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, or 1-16 residuedifferences at other amino acid residue positions as compared to thecorresponding domain or region of a reference sequence based on SEQ IDNO:2, 4 or 86. In some embodiments, the number of differences can be 1,2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, or about 16 residuedifferences at other amino acid residues in the domain. In someembodiments, the differences comprise conservative mutations. In someembodiments, the ketoreductase region or domain comprises an amino acidsequence having at least the preceding feature, and wherein the aminoacid sequence has at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identity as compared to the amino acidsequence corresponding to residues 1-89 of a reference sequence based onSEQ ID NO:2, 4 or 86 having the preceding features.

In some embodiments, the ketoreductase polypeptide can further comprisea domain or region corresponding to residues 212-252 of the sequenceformula of SEQ ID NO:83, 84 or 87, where the domain or region can haveone or more of the following features: residue corresponding to X226 isa non-polar or aliphatic residue; residue corresponding to X248 is anon-polar or basic residue; and residue corresponding to X249 is anaromatic residue. In some embodiments, the polypeptides comprising aregion or domain corresponding to residues 212-252 of the sequenceformula of SEQ ID NO:83, 84 or 87 can have additionally one or moreresidue differences at residue positions not specified by X above ascompared to the reference sequence of SEQ ID NO: 2, 4 or 86. In someembodiments, the differences can be 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8,1-9, or 1-10 residue differences at other amino acid residue positionsnot defined by X above as compared to the reference sequence of SEQ IDNO: 2, 4 or 86. In some embodiments, the number of differences can be 1,2, 3, 4, 5, 6, 7, 8, 9, or 10 residue differences at other amino acidresidue positions. In some embodiments, the differences compriseconservative mutations.

In some embodiments, the ketoreductase polypeptide can further comprisea domain or region corresponding to residues 212-252 of the sequenceformula of SEQ ID NO:83, 84 or 87, where the domain or region can haveone or more of the following features: residue corresponding to X226 isglycine, methionine, alanine, valine, leucine or isoleucine,particularly valine; residue corresponding to X248 is glycine,methionine, alanine, valine, leucine, isoleucine, lysine, or arginine,particularly glycine, lysine, or arginine; and residue corresponding toX249 is tyrosine, phenylalanine, or tryptophan, particularly tyrosine ortryptophan. In some embodiments, the polypeptides comprising a region ordomain corresponding to residues 212-252 of the sequence formula of SEQID NO:83, 84 or 87 can have additionally one or more residue differencesat residue positions not specified by X above as compared to thereference sequence of SEQ ID NO: 2, 4 or 86. In some embodiments, thedifferences can be 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, or 1-10residue differences at other amino acid residue positions not defined byX above as compared to the reference sequence of SEQ ID NO: 2, 4 or 86.In some embodiments, the number of differences can be 1, 2, 3, 4, 5, 6,7, 8, 9, or 10 residue differences at other amino acid residuepositions. In some embodiments, the differences comprise conservativemutations.

In some embodiments, the ketoreductase polypeptide can further comprisea domain or region corresponding to residues 212-252 of the sequenceformula of SEQ ID NO:83, 84 or 87, where the domain or region has atleast the following feature: residue corresponding to X226 is anon-polar or aliphatic residue, particularly valine. In someembodiments, the polypeptide comprising a region or domain correspondingto residues 212-252 of the sequence formula of SEQ ID NO:83, 84 or 87,can have additionally one or more residue differences at other residuepositions as compared to the reference sequence of SEQ ID NO: 2, 4 or 86having the preceding features. In some embodiments, the region or domaincorresponding to residues 212-252 can have additionally 1-2, 1-3, 1-4,1-5, 1-6, 1-7, 1-8, 1-9, or 1-10 residue differences at other amino acidresidue positions as compared to the corresponding domain of thereference sequence based on SEQ ID NO:2, 4 or 86. In some embodiments,the number of differences can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or about 10residue differences at other amino acid residues in the domain. In someembodiments, the differences comprise conservative mutations. In someembodiments, the ketoreductase region or domain comprises an amino acidsequence having at least the preceding features, and wherein the aminoacid sequence has at least 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identity as compared to the amino acidsequence corresponding to residues 212-252 of a reference sequence basedon SEQ ID NO:2, 4 or 86 having the preceding features.

Table 2 below provides exemplary 2S,3R selective ketoreductases, SEQ IDNOs: 1-62, with their associated activities. The sequences below arederived from the wild-type L. kefir ketoreductase sequences (SEQ ID NO:3 and 4) unless otherwise specified. In Table 2 below, each row liststwo SEQ ID NOs, where the odd number refers to the nucleotide sequencethat codes for the amino acid sequence provided by the even number. Thecolumn listing the # of mutations is with respect to the number of aminoacid substitutions as compared to the L. kefir KRED amino acid sequenceof SEQ ID NO:4, and the specific substitutions are listed in the column“mutations from kefir.” In the activity column, one “+” corresponds to a1-15 fold improvement as compared to the ability of the polypeptidehaving the amino acid sequence of SEQ ID NO:48 to convert the substrateto the product of formula (II). Two plus signs “++” indicates that thepolypeptide is about 15 to 30 fold improved as compared to SEQ ID NO:48.Three plus signs “+++” indicates that the polypeptide is about 30 to 40fold improved as compared to SEQ ID NO:48. Four plus signs “++++”indicates that the polypeptide is about 40 to 50 fold improved ascompared to SEQ ID NO:48, and five plus signs “+++++” indicates that thepolypeptide is greater than 50 fold improved as compared to SEQ IDNO:48. A “+” sign under the stability column indicates that thepolypeptide is capable of retaining enzymatic activity for convertingthe substrate to the product of formula (II) after 21 hours of heattreatment at 40° C. For the selectivity column, a single plus sign “+”indicates that the polypeptide is able to convert the substrate to theproduct of formula (II) with about 60-89% stereomeric excess; two plussigns “++” indicates that the polypeptide is able to convert thesubstrate to the product of formula (II) with about 90-94% stereomericexcess; three plus signs “+++” indicates that the polypeptide is able toconvert the substrate to the product of formula (II) with about 95-99%stereomeric excess; and four plus signs “+++” indicates that thepolypeptide is able to convert the substrate to the product of formula(II) with greater than about 99% stereomeric excess. Accordingly, insome embodiments, the 2S,3R selective ketoreductases can comprise asequence corresponding to SEQ ID NO: 6, 8, 10, 12, 14, 16, 18, 20, 22,24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58,60, or 62.

TABLE 2 Table 2: List of Sequences and Corresponding ActivityImprovement Residue # of SEQ Differences from mutations Stabi- Selec- IDNO SEQ ID NO: 2 from kefir Activity lity tivity  1/2 L. brevis  3/4 L.kefir 47/48 A202V  1 improved + over wt 37/38 A94T; E105G; L153A;  6 + +L199A; A202L; M206F 15/16 A94T; S96F; A202V  3 + +++ 55/56 L153A; L199A;A202L  3 + +++ 57/58 T86I; L199N; A202L  3 + +++ 51/52 L153A; A202L  2 ++++ 53/54 L153A; A202V  2 + + 31/32 A94T; L199A; A202V  3 ++ ++++ 33/34A94T; L153A; L199H;  4 +++ ++++ A202L 49/50 L153A; L199H; A202L  3 +++++ 19/20 A94T; L199N; A202V  3 +++ ++++ 45/46 L153S; A202L  2 + + 35/36A94T; L153A; L199A;  4 + ++ A202V 25/26 A94T; A202L  2 +++ +++ 27/28A94T; A202V  2 ++ +++ 29/30 A94T; L199A; A202L  3 +++ ++++ 21/22 A94T;L199H; A202L  3 ++++ ++++ 23/24 A94T; L199H; A202V  3 +++ ++++ 41/42L153A; L199N; A202L  3 + +++ 39/40 A94T; S96F; M129T;  5 + ++ A202V;M206F 17/18 A80T; L153A; A202V;  3 + +++ 43/44 F147M; A202V  2 + +  9/10H40R; A94T; F147L;  5 +++++ + ++++ L199H; A202L 11/12 H40R; A94T; L199H; 4 +++++ ++++ A202L  5/6 A94T; F147L; L199H;  4 +++++ + ++++ A202L  7/8A94T; L199H; A202L  3 +++++ ++++ 59/60 I11F; H40R; A94F; 11 ++++ ++++S96V; F147M; L195V; V196L; L199W; I226V; G248K; Y249W 61/62 T2A; R4C;H40R; 11 +++ ++++ A94G; S96V; F147M; V196L; L199W; I226V; G248K; Y249W13/14 H40R; A94F; S96V;  9 ++++ ++++ F147M; L195V; V196L; L199W; I226V;Y249W

In some embodiments, an improved 2S,3R selective ketoreductase comprisesan amino acid sequence that is at least about 85%, 86%, 87%, 88%, 89%,90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identical to areference sequence based on SEQ ID NO: 6, 8, 10, 12, 14, 16, 18, 20, 22,24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58,60, or 62, with the proviso that the ketoreductase amino acid sequencehas at least the following features: residue corresponding to X94 is analiphatic or polar residue, particularly alanine or threonine; residuecorresponding to X199 is an aliphatic, constrained or polar residue,particularly alanine, histidine, or asparagine; and residuecorresponding to X202 is valine or leucine. In some embodiments, theketoreductase polypeptides can have additionally 1-2, 1-3, 1-4, 1-5,1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12, 1-14, 1-15, 1-16, 1-18, 1-20,1-22, 1-24, 1-25, 1-30, 1-35 or about 1-40 residue differences at otheramino acid residue positions as compared to the reference sequence. Insome embodiments, the number of differences can be 1, 2, 3, 4, 5, 6, 7,8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24, 26, 30, 35 or about 40residue differences at other amino acid residues. In some embodiments,the differences comprise conservative mutations.

In some embodiments, an improved 2S,3R selective ketoreductase comprisesan amino acid sequence that is at least about 85%, 86%, 87%, 88%, 89%,90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identical to areference sequence based on SEQ ID NO: 6, 8, 10, 12, 14, 16, 18, 20, 22,24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58,60, or 62, with the proviso that the ketoreductase amino acid sequencecomprises any one of the set of mutations contained in any one of thepolypeptide sequences listed in Table 2 as compared to SEQ ID NO:2 or 4or 86. In some embodiments, the ketoreductase polypeptides can haveadditionally 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12,1-14, 1-15, 1-16, 1-18, 1-20, 1-22, 1-24, 1-25, 1-30, 1-35 or about 1-40residue differences at other amino acid residue positions as compared tothe reference sequence. In some embodiments, the number of differencescan be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22,24, 26, 30, 35 or about 40 residue differences at other amino acidresidues. In some embodiments, the differences comprise conservativemutations.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S, 3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, with apercent stereomeric excess of at least about 85% or with a percentstereomeric excess that is greater than the wild-type L. kefir KRED (SEQID NO:4). Exemplary polypeptides that are capable include, but are notlimited to, polypeptides comprising an amino acid sequence correspondingto SEQ ID NO: 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34,36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, or 62.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S, 3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, with apercent stereomeric excess of at least about 60-89% and at a rate thatis at least about 1-15 fold greater than the rate capable by thepolypeptide having the amino acid sequence of SEQ ID NO:48. Exemplarypolypeptides that are capable include, but are not limited to,polypeptides comprising an amino acid sequence corresponding to SEQ IDNO: 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38,40, 42, 46, 50, 52, 54, 56, 58, 60, or 62. Because the referencepolypeptide having the amino acid sequence of SEQ ID NO:48 is capable ofconverting the substrate to the product at a rate (for example, 100%conversion in 20 hours of 1 g/L substrate with about 10 g/L of the KRED,in 50% IPA at pH 8) and with a steroselectivity that is improved overwild-type (SEQ ID NO:4), the polypeptides herein that are improved overSEQ ID NO:48 are also improved over wild-type.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S, 3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, with apercent stereomeric excess of at least about 90-94%. Exemplarypolypeptides that are capable include, but are not limited to,polypeptides comprising an amino acid sequence corresponding to SEQ IDNO: 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 40,42, 50, 52, 56, 58, 60, or 62.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S, 3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, with apercent stereomeric excess of at least about 95-99%. Exemplarypolypeptides that are capable include, but are not limited to,polypeptides comprising an amino acid sequence corresponding to SEQ IDNO: 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 42, 50,52, 56, 58, 60, or 62.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S, 3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, with apercent stereomeric excess of at least about 99%. Exemplary polypeptidesthat are capable include, but are not limited to, polypeptidescomprising an amino acid sequence corresponding to SEQ ID NO:6, 8, 10,12, 14, 20, 22, 24, 30, 32, 34, 60, or 62.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S, 3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a ratethat is at least about 15-30 fold greater than the rate capable by thepolypeptide having the amino acid sequence of SEQ ID NO:48. Exemplarypolypeptides that are capable include, but are not limited to,polypeptides comprising an amino acid sequence corresponding to SEQ IDNO: 6, 8, 10, 12, 14, 20, 22, 24, 26, 28, 30, 32, 34, 50, 60, or 62.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S, 3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a ratethat is at least about 30-40 fold greater than the rate capable by thepolypeptide having the amino acid sequence of SEQ ID NO:48. Exemplarypolypeptides that are capable include, but are not limited to,polypeptides comprising an amino acid sequence corresponding to SEQ IDNO: 6, 8, 10, 12, 14, 20, 22, 24, 26, 30, 34, 60, or 62.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S, 3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a ratethat is at least about 40-50 fold greater than the rate capable by thepolypeptide having the amino acid sequence of SEQ ID NO:48. Exemplarypolypeptides that are capable include, but are not limited to,polypeptides comprising an amino acid sequence corresponding to SEQ IDNO: 6, 8, 10, 12, 14, 22, or 60.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a ratethat is at least about 50 fold greater than the rate capable by thepolypeptide having the amino acid sequence of SEQ ID NO:48. Exemplarypolypeptides that are capable include, but are not limited to,polypeptides comprising an amino acid sequence corresponding to SEQ IDNO: 6, 8, 10, or 12.

In some embodiments, the ketoreductase polypeptides are capable ofconverting the substrate, methyl-2-benzamidomethyl-3-oxobutyrate, to theproduct, 2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a ratethat is at least about 50 fold greater than the rate capable by thepolypeptide having the amino acid sequence of SEQ ID NO:48 and with astereomeric excess of at least 99%. Exemplary polypeptides that arecapable include, but are not limited to, polypeptides comprising anamino acid sequence corresponding to SEQ ID NO: 6, 8, 10, and 12.

In some embodiments, the ketoreductase polypeptide are capable ofretaining its ability to convert the substrate,methyl-2-benzamidomethyl-3-oxobutyrate, to the product,2S,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, after heat treatmentat 40° C. for 21 hours. Exemplary polypeptides that are capable include,but are not limited to, polypeptides comprising an amino acid sequencecorresponding to SEQ ID NO: 6, 10, or 44.

As noted above, in some embodiments, the ketoreductases arestereoselectively capable of reducing or converting the substrate offormula (I) to the product of formula (III). Table 3 below providesexemplary 2R,3R specific ketoreductases, SEQ ID NOs 63-82, with theirassociated activities. The sequences below are derived from thewild-type L. kefir ketoreductase sequences (SEQ ID NO: 3 and 4) unlessotherwise specified. In Table 3 below, each row lists two SEQ ID NOs,where the odd number refers to the nucleotide sequence that codes forthe amino acid sequence provided by the even number. The column listingthe # of mutations is with respect to the number of amino acidsubstitutions as compared to the L. kefir KRED amino acid sequence ofSEQ ID NO:4, and the column “sequence—coding mutations” lists thesubstitutions as compared to SEQ ID NO:4. In the activity column, one“+” corresponds to an about 1 fold improvement as compared to theability of the polypeptide having the amino acid sequence of SEQ IDNO:66 to convert the substrate to the product of formula (III). Two plussigns “++” indicates that the polypeptide is greater than about 1 to 2fold improved as compared to SEQ ID NO:66. Three plus signs “+++”indicates that the polypeptide is greater than about 5 fold improved ascompared to SEQ ID NO:66. For the selectivity column, a single plus sign“+” indicates that the polypeptide is able to convert the substrate tothe product of formula (III) with less than about 85% stereomericexcess; two plus signs “++” indicates that the polypeptide is able toconvert the substrate to the product of formula (III) with greater thanabout 85% stereomeric excess. Accordingly, in some embodiments, the2S,3R selective ketoreductases can comprise a sequence corresponding toSEQ ID NO: 64, 66, 68, 70, 72, 74, 76, 78, 80, or 82.

TABLE 3 List of Sequences and Corresponding Activity Improvement # ofResidue Differences from mutations SEQ ID NO SEQ ID NO: 4 from kefirActivity Stability 65/66 H40R; A94G; S96V; E145F; 10 + + F147M; Y190P;V196L; L199W; I226V; Y249W 73/74 I11F; H40R; A94E; 12 ++ ++ S96V; E145F;F147M; Y190P; L195V; V196L; L199W; I226V; Y249H 81/82 D3V; A10T; H40R;12 + ++ A94G; S96V; F147M; Y190P; V196L; L199W; I226V; G248K; Y249H67/68 H40R; A94F; S96V; 12 ++ ++ E145F; F147M; Y190P; L195V; V196L;L199W; I226V; G248R; Y249W 77/78 I11L; H40R; A94E; S96V; 10 +++ ++F147M; Y190H; V196L; I226V; G248K; Y249H 71/72 H40R; T54A; A94F; S96V;11 +++ ++ E105K; E145D; F147M; V196L; L199W; I226V; Y249W 75/76 I11F;H40R; A94G; S96V; 14 +++ ++ E145F; F147M; Y190H; L195V; V196L; L199W;A202V; I226V; Y249H; A251T 69/70 H40R; E78D; A94E; 11 +++ + S96V; F147M;Y190H; L195V; V196L; I226V; Y249H; T250Y 79/80 K8N; V9G; I11F; 13 +++ +H40R; A94G; S96V; E145F; F147M; Y190P; V196L; I226V; G248K; Y249R 63/64V12I; H40R; A94E; 12 +++ + S96V; F147M; Y190P; L195V; V196L; L199W;I226V; G248R; Y249W

In some embodiments, an improved 2R,3R selective ketoreductase comprisesan amino acid sequence that is at least about 85%, 86%, 87%, 88%, 89%,90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identical to areference sequence based on SEQ ID NO: 64, 66, 68, 70, 72, 74, 76, 78,80, or 82, with the proviso that the ketoreductase amino acid sequencecomprises any one of the set of mutations contained in any one of thepolypeptide sequences listed in Table 3 as compared to SEQ ID NO:2 or 4or 86. In some embodiments, the ketoreductase polypeptides can haveadditionally 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12,1-14, 1-15, 1-16, 1-18, 1-20, 1-22, 1-24, 1-25, 1-30, 1-35 or about 1-40residue differences at other amino acid residue positions as compared tothe reference sequence. In some embodiments, the number of differencescan be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22,24, 26, 30, 35 or about 40 residue differences at other amino acidresidues. In some embodiments, the differences comprise conservativemutations.

In some embodiments, the 2R,3R selective ketoreductase polypeptides arecapable of converting the substrate,methyl-2-benzamidomethyl-3-oxobutyrate, to the product,2R,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, with a percentstereomeric excess of at least about 85%. Exemplary polypeptides thatare capable include, but are not limited to, polypeptides comprising anamino acid sequence corresponding to SEQ ID NO: 68, 72, 74, 76, 78, or82.

In some embodiments, the 2R,3R selective ketoreductase polypeptides arecapable of converting the substrate,methyl-2-benzamidomethyl-3-oxobutyrate, to the product,2R,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a rate that is atleast about 1 fold greater than the rate capable by the polypeptidehaving the amino acid sequence of SEQ ID NO:66. Exemplary polypeptidesthat are capable include, but are not limited to, polypeptidescomprising an amino acid sequence corresponding to SEQ ID NO: 64, 68,70, 72, 74, 76, 78. 80, or 82. Because the polypeptide having the aminoacid sequence of SEQ ID NO:66 is capable of capable of converting thesubstrate, methyl-2-benzamidomethyl-3-oxobutyrate, to the product,2R,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, with a stereomericexcess and at a rate that is greater than wild-type L. kefir KRED (SEQID NO:4), any polypeptide improved over SEQ ID NO:66 is also improvedover wild-type L. kefir KRED.

In some embodiments, the 2R,3R selective ketoreductase polypeptidecapable of converting the substrate,methyl-2-benzamidomethyl-3-oxobutyrate, to the product,2R,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a rate that is atleast about 1-2 fold greater than the rate capable by the polypeptidehaving the amino acid sequence of SEQ ID NO:66. Exemplary polypeptidesthat are capable include, but are not limited to, polypeptidescomprising an amino acid sequence corresponding to SEQ ID NO: 64, 68,70, 72, 74, 76, 78. or 80.

In some embodiments, the 2R,3R selective ketoreductase polypeptides arecapable of converting the substrate,methyl-2-benzamidomethyl-3-oxobutyrate, to the product, 2R,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a rate that is atleast about 5 fold greater than the rate capable by the polypeptidehaving the amino acid sequence of SEQ ID NO:66. Exemplary polypeptidesthat are capable include, but are not limited to, polypeptidescomprising an amino acid sequence corresponding to SEQ ID NO: 64, 70,72, 76, 78. or 80.

In some embodiments, the 2R,3R selective ketoreductase polypeptides arecapable of converting the substrate,methyl-2-benzamidomethyl-3-oxobutyrate, to the product,2R,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, at a rate that is atleast about 5 fold greater than the rate capable by the polypeptidehaving the amino acid sequence of SEQ ID NO:66 and with a stereomericexcess that is at least 85%. Exemplary polypeptides that are capableinclude, but are not limited to, polypeptides comprising an amino acidsequence corresponding to SEQ ID NO: 72 or 78.

In some embodiments, the 2S,3R selective ketoreductase polypeptides ofthe disclosure can comprise an amino acid sequence that is at leastabout 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%,98%, or 99% identical to SEQ ID NO:2 or SEQ ID NO:4 or SEQ ID NO:86 (ora region or domain thereof, such as residues 90-211) with the provisothat the residues corresponding to residue 202 of SEQ ID NO:2 or SEQ IDNO:4 or SEQ ID NO:86 is a valine or leucine, the residue correspondingto residue 94 of SEQ ID NO:2 or 4 or 86 is threonine, and the residuecorresponding to residue 199 of SEQ ID NO:2 or 4 or 86 is histidine, andadditionally has one or more of the following substitutions such thatthe polypeptide is further improved (with respect to stereoselectivity,enzymatic activity, and/or thermostability) over the wild-type kefirketoreductase or another engineered ketoreductase (such as SEQ IDNO:48): 2→A; 4→C; 11→F; 40→H; 80→T; 86→4; 96→F, V; 105→G; 129→T; 147→M,L; 153→A, S; 195→V; 196→L; 206→F; 226→V; 248→K; and 249→W.

In some embodiments, the 2S,3R ketoreductase polypeptides describedherein can comprise an amino acid sequence that is at least about 85%,86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%identical to SEQ ID NO:2, 4 or 86 (or a region or domain thereof, suchas residues 90-211) with the proviso that the residues corresponding toresidue 202 of SEQ ID NO:2, 4 or 86 is a valine or leucine, the residuecorresponding to residue 94 of SEQ ID NO:2, 4 or 86 is threonine, andthe residue corresponding to residue 199 of SEQ ID NO:2, 4 or 86 ishistidine, and additionally has one or more of the followingsubstitutions such that the polypeptide is further improved (withrespect to stereoselectivity, enzymatic activity, and/orthermostability) over the wild-type kefir ketoreductase or anotherengineered ketoreductase (such as SEQ ID NO:48): 40→H; and 147→L, M.

As will be appreciated by those of skill in the art, some of theabove-defined categories of amino acid residues, unless otherwisespecified, are not mutually exclusive. Thus, amino acids having sidechains exhibiting two or more physico-chemical properties can beincluded in multiple categories. The appropriate classification of anyamino acid or residue will be apparent to those of skill in the art,especially in light of the detailed disclosure provided herein.

In some embodiments, the improved engineered ketoreductase enzymescomprise deletions of the naturally occurring ketoreductase polypeptidesor deletions of other engineered ketoreductase polypeptides. In someembodiments, each of the improved engineered ketoreductase enzymesdescribed herein can comprise deletions of the polypeptides describedherein. Thus, for each and every embodiment of the ketoreductasepolypeptides of the disclosure, the deletions can comprise one or moreamino acids, 2 or more amino acids, 3 or more amino acids, 4 or moreamino acids, 5 or more amino acids, 6 or more amino acids, 8 or moreamino acids, 10 or more amino acids, 15 or more amino acids, or 20 ormore amino acids, up to 10% of the total number of amino acids, up to10% of the total number of amino acids, up to 20% of the total number ofamino acids, or up to 30% of the total number of amino acids of theketoreductase polypeptides, as long as the functional activity of theketoreductase activity is maintained. In some embodiments, the deletionscan comprise, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12,1-14, 1-15, 1-16, 1-18, 1-20, 1-22, 1-24, 1-25, 1-30, 1-35 or about 1-40amino acid residues. In some embodiments, the number of deletions can be1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 20, 22, 24, 26,30, 35 or about 40 amino acids. In some embodiments, the deletions cancomprise deletions of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,16, 18, or 20 amino acid residues.

As described herein, the ketoreductase polypeptides of the disclosurecan be in the form of fusion polypeptides in which the ketoreductasepolypeptides are fused to other polypeptides, such as, by way of exampleand not limitation, antibody tags (e.g., myc epitope), purificationssequences (e.g., His tags), and cell localization signals (e.g.,secretion signals). Thus, the ketoreductase polypeptides can be usedwith or without fusions to other polypeptides.

The polypeptides described herein are not restricted to the geneticallyencoded amino acids. In addition to the genetically encoded amino acids,the polypeptides described herein may be comprised, either in whole orin part, of naturally-occurring and/or synthetic non-encoded aminoacids. Certain commonly encountered non-encoded amino acids of which thepolypeptides described herein may be comprised include, but are notlimited to: the D-stereomers of the genetically-encoded amino acids;2,3-diaminopropionic acid (Dpr); α-aminoisobutyric acid (Aib);ε-aminohexanoic acid (Aha); δ-aminovaleric acid (Ava); N-methylglycineor sarcosine (MeGly or Sar); ornithine (Orn); citrulline (Cit);t-butylalanine (Bua); t-butylglycine (Bug); N-methylisoleucine (MeIle);phenylglycine (Phg); cyclohexylalanine (Cha); norleucine (Nle);naphthylalanine (Nal); 2-chlorophenylalanine (Oct);3-chlorophenylalanine (Mcf); 4-chlorophenylalanine (Pcf);2-fluorophenylalanine (Off); 3-fluorophenylalanine (Mff);4-fluorophenylalanine (Pff); 2-bromophenylalanine (Obf);3-bromophenylalanine (Mbf); 4-bromophenylalanine (Pbf);2-methylphenylalanine (Omf); 3-methylphenylalanine (Mmf);4-methylphenylalanine (Pmf); 2-nitrophenylalanine (Onf);3-nitrophenylalanine (Mnf); 4-nitrophenylalanine (Pnf);2-cyanophenylalanine (Oct); 3-cyanophenylalanine (Mcf);4-cyanophenylalanine (Pcf); 2-trifluoromethylphenylalanine (Ott);3-trifluoromethylphenylalanine (Mtf); 4-trifluoromethylphenylalanine(Ptf); 4-aminophenylalanine (Pat); 4-iodophenylalanine (Pit);4-aminomethylphenylalanine (Pamf); 2,4-dichlorophenylalanine (Opef);3,4-dichlorophenylalanine (Mpcf); 2,4-difluorophenylalanine (Opff);3,4-difluorophenylalanine (Mpff); pyrid-2-ylalanine (2pAla);pyrid-3-ylalanine (3pAla); pyrid-4-ylalanine (4pAla); naphth-1-ylalanine(1nAla); naphth-2-ylalanine (2nAla); thiazolylalanine (taAla);benzothienylalanine (bAla); thienylalanine (tAla); furylalanine (fAla);homophenylalanine (hPhe); homotyrosine (hTyr); homotryptophan (hTrp);pentafluorophenylalanine (5ff); styrylkalanine (sAla); authrylalanine(aAla); 3,3-diphenylalanine (Dfa); 3-amino-5-phenypentanoic acid (Afp);penicillamine (Pen); 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid(Tic); β-2-thienylalanine (Thi); methionine sulfoxide (Mso);N(w)-nitroarginine (nArg); homolysine (hLys);phosphonomethylphenylalanine (pmPhe); phosphoserine (pSer);phosphothreonine (pThr); homoaspartic acid (hAsp); homoglutanic acid(hGlu); 1-aminocyclopent-(2 or 3)-ene-4 carboxylic acid; pipecolic acid(PA), azetidine-3-carboxylic acid (ACA);1-aminocyclopentane-3-carboxylic acid; allylglycine (aOly);propargylglycine (pgGly); homoalanine (hAla); norvaline (nVal);homoleucine (hLeu), homovaline (hVal); homoisolencine (hlle);homoarginine (hArg); N-acetyl lysine (AcLys); 2,4-diaminobutyric acid(Dbu); 2,3-diaminobutyric acid (Dab); N-methylvaline (MeVal);homocysteine (hCys); homoserine (hSer); hydroxyproline (Hyp) andhomoproline (hPro). Additional non-encoded amino acids of which thepolypeptides described herein may be comprised will be apparent to thoseof skill in the art (see, e.g., the various amino acids provided inFasman, 1989, CRC Practical Handbook of Biochemistry and MolecularBiology, CRC Press, Boca Raton, Fla., at pp. 3-70 and the referencescited therein, all of which are incorporated by reference). These aminoacids may be in either the L- or D-configuration.

Those of skill in the art will recognize that amino acids or residuesbearing side chain protecting groups may also comprise the polypeptidesdescribed herein. Non-limiting examples of such protected amino acids,which in this case belong to the aromatic category, include (protectinggroups listed in parentheses), but are not limited to: Arg(tos),Cys(methylbenzyl), Cys (nitropyridinesulfenyl), Glu(δ-benzylester),Gln(xanthyl), Asn(N-δ-xanthyl), His(bom), His(benzyl), His(tos),Lys(fmoc), Lys(tos), Ser(O-benzyl), Thr (O-benzyl) and Tyr(O-benzyl).

Non-encoding amino acids that are conformationally constrained of whichthe polypeptides described herein may be composed include, but are notlimited to, N-methyl amino acids (L-configuration); 1-aminocyclopent-(2or 3)-ene-4-carboxylic acid; pipecolic acid; azetidine-3-carboxylicacid; homoproline (hPro); and 1-aminocyclopentane-3-carboxylic acid.

As described above the various modifications introduced into thenaturally occurring polypeptide to generate an engineered ketoreductaseenzyme can be targeted to a specific property of the enzyme.

1.3 Polynucleotides Encoding Engineered Ketoreductases

In another aspect, the present disclosure provides polynucleotidesencoding the engineered ketoreductase enzymes. The polynucleotides maybe operatively linked to one or more heterologous regulatory sequencesthat control gene expression to create a recombinant polynucleotidecapable of expressing the polypeptide. Expression constructs containinga heterologous polynucleotide encoding the engineered ketoreductase canbe introduced into appropriate host cells to express the correspondingketoreductase polypeptide.

Because of the knowledge of the codons corresponding to the variousamino acids, availability of a protein sequence provides a descriptionof all the polynucleotides capable of encoding the subject. Thedegeneracy of the genetic code, where the same amino acids are encodedby alternative or synonymous codons allows an extremely large number ofnucleic acids to be made, all of which encode the improved ketoreductaseenzymes disclosed herein. Thus, having identified a particular aminoacid sequence, those skilled in the art could make any number ofdifferent nucleic acids by simply modifying the sequence of one or morecodons in a way which does not change the amino acid sequence of theprotein. In this regard, the present disclosure specificallycontemplates each and every possible variation of polynucleotides thatcould be made by selecting combinations based on the possible codonchoices, and all such variations are to be considered specificallydisclosed for any polypeptide disclosed herein, including the amino acidsequences presented in Table 1.

In various embodiments, the codons are preferably selected to fit thehost cell in which the protein is being produced. For example, preferredcodons used in bacteria are used to express the gene in bacteria;preferred codons used in yeast are used for expression in yeast; andpreferred codons used in mammals are used for expression in mammaliancells. By way of example, the polynucleotide of SEQ ID NO: 1 has beencodon optimized for expression in E. coli, but otherwise encodes thenaturally occurring ketoreductase of Lactobacillus kefir.

In certain embodiments, all codons need not be replaced to optimize thecodon usage of the ketoreductases since the natural sequence willcomprise preferred codons and because use of preferred codons may not berequired for all amino acid residues. Consequently, codon optimizedpolynucleotides encoding the ketoreductase enzymes may contain preferredcodons at about 40%, 50%, 60%, 70%, 80%, or greater than 90% of codonpositions of the full length coding region.

In some embodiments, the polynucleotide comprises a nucleotide sequenceencoding a ketoreductase polypeptide with an amino acid sequence thathas at least about 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% or more sequence identity to any of thereference engineered ketoreductase polypeptides described herein.Accordingly, in some embodiments, the polynucleotide encodes an aminoacid sequence that is at least about 80%, 85%, 86%, 87%, 88%, 89%, 90%,91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more identical to areference sequence based on SEQ ID NO: 2, 4 or 86 having the followingfeatures: residue corresponding to position X94 is an aliphatic or polarresidue, particularly alanine or threonine; residue corresponding toX199 is an aliphatic, constrained or polar residue, particularlyalanine, histidine, or asparagine; and residue corresponding to X202 isvaline or leucine, with the proviso that the encoded ketoreductasepolypeptide has an amino sequence having the preceding features, i.e.,residue corresponding to position X94 is an aliphatic or polar residue;residue corresponding to X199 is an aliphatic, constrained or polarresidue; and residue corresponding to X202 is valine or leucine. In someembodiments, the polynucleotide encodes a ketoreductase that has anamino acid sequence in which the residue corresponding to X94 isthreonine; residue corresponding to X199 is alanine, histidine, orasparagine; and residue corresponding to X202 is valine or leucine. Insome embodiments, the polynucleotide encodes an amino acid sequencecorresponding to SEQ ID NO: 6, 8, 10, 12, 16, 18, 20, 22, 24, 26, 28,30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, or 58.

In some embodiments, the polynucleotide comprises a nucleotide sequenceencoding a ketoreductase polypeptide with an amino acid sequence thathas at least about 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% or more sequence identity to thepolypeptide comprising an amino acid corresponding to SEQ ID NO:14, 60,or 62.

In some embodiments, the polynucleotide comprises a nucleotide sequenceencoding a ketoreductase polypeptide with an amino acid sequence thathas at least about 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% or more sequence identity to thepolypeptide comprising an amino acid sequence corresponding to SEQ IDNO: 64, 66, 68, 70, 72, 74, 76, 78, 80 or 82.

In some embodiments, the polynucleotides encoding the ketoreductases areselected from SEQ ID NO: 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27,29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63,65, 67, 69, 71, 73, 75, 77, 79, or 81. In some embodiments, thepolynucleotides are capable of hybridizing under highly stringentconditions to a polynucleotide comprising SEQ ID NO: 5, 7, 9, 11, 13,15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49,51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, or 81, wherethe highly stringently hybridizing polynucleotides encode aketoreductase capable of stereoselectively reducing or converting thesubstrate of formula (I) to the product of formula (II), orstereoselectively reducing or converting the substrate of formula (I) tothe product of formula (III).

In some embodiments, the polynucleotides encode the polypeptidesdescribed herein but have about 80% or more sequence identity, about85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or99% or more sequence identity at the nucleotide level to a referencepolynucleotide encoding the engineered ketoreductase. In someembodiments, the reference polynucleotide is selected from SEQ ID NO: 5,7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41,43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77,79, or 81.

An isolated polynucleotide encoding an improved ketoreductasepolypeptide may be manipulated in a variety of ways to provide forexpression of the polypeptide. Manipulation of the isolatedpolynucleotide prior to its insertion into a vector may be desirable ornecessary depending on the expression vector. The techniques formodifying polynucleotides and nucleic acid sequences utilizingrecombinant DNA methods are well known in the art. Guidance is providedin Sambrook et al., 2001, Molecular Cloning: A Laboratory Manual, 3^(rd)Ed., Cold Spring Harbor Laboratory Press; and Current Protocols inMolecular Biology, Ausubel. F. ed., Greene Pub. Associates, 1998,updates to 2006.

For bacterial host cells, suitable promoters for directing transcriptionof the nucleic acid constructs of the present disclosure, include thepromoters obtained from the E. coli lac operon, E. coli trp operon,bacteriophage □, Streptomyces coelicolor agarase gene (dagA), Bacillussubtilis levansucrase gene (sacB), Bacillus licheniformis alpha-amylasegene (amyL), Bacillus stearothermophilus maltogenic amylase gene (amyM),Bacillus amyloliquefaciens alpha-amylase gene (amyQ), Bacilluslicheniformis penicillinase gene (penP), Bacillus subtilis xylA and xylBgenes, and prokaryotic beta-lactamase gene (Villa-Kamaroff et al., 1978,Proc. Natl Acad. Sci. USA 75: 3727-3731), as well as the tac promoter(DeBoer et al., 1983, Proc. Natl Acad. Sci. USA 80: 21-25). Furtherpromoters are described in “Useful proteins from recombinant bacteria”in Scientific American, 1980, 242:74-94; and in Sambrook et al., supra.

For filamentous fungal host cells, suitable promoters for directing thetranscription of the nucleic acid constructs of the present disclosureinclude promoters obtained from the genes for Aspergillus oryzae TAKAamylase, Rhizomucor miehei aspartic proteinase, Aspergillus nigerneutral alpha-amylase, Aspergillus niger acid stable alpha-amylase,Aspergillus niger or Aspergillus awamori glucoamylase (glaA), Rhizomucormiehei lipase, Aspergillus oryzae alkaline protease, Aspergillus oryzaetriose phosphate isomerase, Aspergillus nidulans acetamidase, andFusarium oxysporum trypsin-like protease (WO 96/00787), as well as theNA2-tpi promoter (a hybrid of the promoters from the genes forAspergillus niger neutral alpha-amylase and Aspergillus oryzae triosephosphate isomerase), and mutant, truncated, and hybrid promotersthereof.

In a yeast host, useful promoters can be from the genes forSaccharomyces cerevisiae enolase (ENO-1), Saccharomyces cerevisiaegalactokinase (GAL1), Saccharomyces cerevisiae alcoholdehydrogenase/glyceraldehyde-3-phosphate dehydrogenase (ADH2/GAP), andSaccharomyces cerevisiae 3-phosphoglycerate kinase. Other usefulpromoters for yeast host cells are described by Romanos et al., 1992,Yeast 8:423-488.

The control sequence may also be a suitable transcription terminatorsequence, a sequence recognized by a host cell to terminatetranscription. The terminator sequence is operably linked to the 3′terminus of the nucleic acid sequence encoding the polypeptide. Anyterminator which is functional in the host cell of choice may be used inthe present invention.

For example, exemplary transcription terminators for filamentous fungalhost cells can be obtained from the genes for Aspergillus oryzae TAKAamylase, Aspergillus niger glucoamylase, Aspergillus nidulansanthranilate synthase, Aspergillus niger alpha-glucosidase, and Fusariumoxysporum trypsin-like protease.

Exemplary terminators for yeast host cells can be obtained from thegenes for Saccharomyces cerevisiae enolase, Saccharomyces cerevisiaecytochrome C (CYC1), and Saccharomyces cerevisiaeglyceraldehyde-3-phosphate dehydrogenase. Other useful terminators foryeast host cells are described by Romanos et al., 1992, supra.

The control sequence may also be a suitable leader sequence, anontranslated region of an mRNA that is important for translation by thehost cell. The leader sequence is operably linked to the 5′ terminus ofthe nucleic acid sequence encoding the polypeptide. Any leader sequencethat is functional in the host cell of choice may be used. Exemplaryleaders for filamentous fungal host cells are obtained from the genesfor Aspergillus oryzae TAKA amylase and Aspergillus nidulans triosephosphate isomerase. Suitable leaders for yeast host cells are obtainedfrom the genes for Saccharomyces cerevisiae enolase (ENO-1),Saccharomyces cerevisiae 3-phosphoglycerate kinase, Saccharomycescerevisiae alpha-factor, and Saccharomyces cerevisiae alcoholdehydrogenase/glyceraldehyde-3-phosphate dehydrogenase (ADH2/GAP).

The control sequence may also be a polyadenylation sequence, a sequenceoperably linked to the 3′ terminus of the nucleic acid sequence andwhich, when transcribed, is recognized by the host cell as a signal toadd polyadenosine residues to transcribed mRNA. Any polyadenylationsequence which is functional in the host cell of choice may be used inthe present invention. Exemplary polyadenylation sequences forfilamentous fungal host cells can be from the genes for Aspergillusoryzae TAKA amylase, Aspergillus niger glucoamylase, Aspergillusnidulans anthranilate synthase, Fusarium oxysporum trypsin-likeprotease, and Aspergillus niger alpha-glucosidase. Usefulpolyadenylation sequences for yeast host cells are described by Guo andSherman, 1995, Mol Cell Bio 15:5983-5990.

The control sequence may also be a signal peptide coding region thatcodes for an amino acid sequence linked to the amino terminus of apolypeptide and directs the encoded polypeptide into the cell'ssecretory pathway. The 5′ end of the coding sequence of the nucleic acidsequence may inherently contain a signal peptide coding region naturallylinked in translation reading frame with the segment of the codingregion that encodes the secreted polypeptide. Alternatively, the 5′ endof the coding sequence may contain a signal peptide coding region thatis foreign to the coding sequence. The foreign signal peptide codingregion may be required where the coding sequence does not naturallycontain a signal peptide coding region.

Alternatively, the foreign signal peptide coding region may simplyreplace the natural signal peptide coding region in order to enhancesecretion of the polypeptide. However, any signal peptide coding regionwhich directs the expressed polypeptide into the secretory pathway of ahost cell of choice may be used in the present invention.

Effective signal peptide coding regions for bacterial host cells are thesignal peptide coding regions obtained from the genes for Bacillus NC1B11837 maltogenic amylase, Bacillus stearothermophilus alpha-amylase,Bacillus licheniformis subtilisin, Bacillus licheniformisbeta-lactamase, Bacillus stearothermophilus neutral proteases (nprT,nprS, nprM), and Bacillus subtilis prsA. Further signal peptides aredescribed by Simonen and Palva, 1993, Microbiol Rev 57: 109-137.

Effective signal peptide coding regions for filamentous fungal hostcells can be the signal peptide coding regions obtained from the genesfor Aspergillus oryzae TAKA amylase, Aspergillus niger neutral amylase,Aspergillus niger glucoamylase, Rhizomucor miehei aspartic proteinase,Humicola insolens cellulase, and Humicola lanuginosa lipase.

Useful signal peptides for yeast host cells can be from the genes forSaccharomyces cerevisiae alpha-factor and Saccharomyces cerevisiaeinvertase. Other useful signal peptide coding regions are described byRomanos et al., 1992, supra.

The control sequence may also be a propeptide coding region that codesfor an amino acid sequence positioned at the amino terminus of apolypeptide. The resultant polypeptide is known as a proenzyme orpropolypeptide (or a zymogen in some cases). A propolypeptide isgenerally inactive and can be converted to a mature active polypeptideby catalytic or autocatalytic cleavage of the propeptide from thepropolypeptide. The propeptide coding region may be obtained from thegenes for Bacillus subtilis alkaline protease (aprE), Bacillus subtilisneutral protease (nprT), Saccharomyces cerevisiae alpha-factor,Rhizomucor miehei aspartic proteinase, and Myceliophthora thermophilalactase (WO 95/33836).

Where both signal peptide and propeptide regions are present at theamino terminus of a polypeptide, the propeptide region is positionednext to the amino terminus of a polypeptide and the signal peptideregion is positioned next to the amino terminus of the propeptideregion.

It may also be desirable to add regulatory sequences, which allow theregulation of the expression of the polypeptide relative to the growthof the host cell. Examples of regulatory systems are those which causethe expression of the gene to be turned on or off in response to achemical or physical stimulus, including the presence of a regulatorycompound. In prokaryotic host cells, suitable regulatory sequencesinclude the lac, tac, and trp operator systems. In yeast host cells,suitable regulatory systems include, as examples, the ADH2 system orGAL1 system. In filamentous fungi, suitable regulatory sequences includethe TAKA alpha-amylase promoter, Aspergillus niger glucoamylasepromoter, and Aspergillus oryzae glucoamylase promoter.

Other examples of regulatory sequences are those which allow for geneamplification. In eukaryotic systems, these include the dihydrofolatereductase gene, which is amplified in the presence of methotrexate, andthe metallothionein genes, which are amplified with heavy metals. Inthese cases, the nucleic acid sequence encoding the KRED polypeptide ofthe present invention would be operably linked with the regulatorysequence.

Thus, in another embodiment, the present disclosure is also directed toa recombinant expression vector comprising a polynucleotide encoding anengineered ketoreductase polypeptide or a variant thereof, and one ormore expression regulating regions such as a promoter and a terminator,a replication origin, etc., depending on the type of hosts into whichthey are to be introduced. The various nucleic acid and controlsequences described above may be joined together to produce arecombinant expression vector which may include one or more convenientrestriction sites to allow for insertion or substitution of the nucleicacid sequence encoding the polypeptide at such sites. Alternatively, thenucleic acid sequence of the present disclosure may be expressed byinserting the nucleic acid sequence or a nucleic acid constructcomprising the sequence into an appropriate vector for expression. Increating the expression vector, the coding sequence is located in thevector so that the coding sequence is operably linked with theappropriate control sequences for expression.

The recombinant expression vector may be any vector (e.g., a plasmid orvirus), which can be conveniently subjected to recombinant DNAprocedures and can bring about the expression of the polynucleotidesequence. The choice of the vector will typically depend on thecompatibility of the vector with the host cell into which the vector isto be introduced. The vectors may be linear or closed circular plasmids.

The expression vector may be an autonomously replicating vector, i.e., avector that exists as an extrachromosomal entity, the replication ofwhich is independent of chromosomal replication, e.g., a plasmid, anextrachromosomal element, a minichromosome, or an artificial chromosome.The vector may contain any means for assuring self-replication.Alternatively, the vector may be one which, when introduced into thehost cell, is integrated into the genome and replicated together withthe chromosome(s) into which it has been integrated. Furthermore, asingle vector or plasmid or two or more vectors or plasmids whichtogether contain the total DNA to be introduced into the genome of thehost cell, or a transposon may be used.

The expression vector of the present invention preferably contains oneor more selectable markers, which permit easy selection of transformedcells. A selectable marker is a gene the product of which provides forbiocide or viral resistance, resistance to heavy metals, prototrophy toauxotrophs, and the like. Examples of bacterial selectable markers arethe dal genes from Bacillus subtilis or Bacillus licheniformis, ormarkers, which confer antibiotic resistance such as ampicillin,kanamycin, chloramphenicol (Example 1) or tetracycline resistance.Suitable markers for yeast host cells are ADE2, HIS3, LEU2, LYS2, MET3,TRP1, and URA3.

Selectable markers for use in a filamentous fungal host cell include,but are not limited to, amdS (acetamidase), argB (ornithinecarbamoyltransferase), bar (phosphinothricin acetyltransferase), hph(hygromycin phosphotransferase), niaD (nitrate reductase), pyrG(orotidine-5′-phosphate decarboxylase), sC (sulfate adenyltransferase),and trpC (anthranilate synthase), as well as equivalents thereof.Embodiments for use in an Aspergillus cell include the amdS and pyrGgenes of Aspergillus nidulans or Aspergillus oryzae and the bar gene ofStreptomyces hygroscopicus.

The expression vectors of the present invention preferably contain anelement(s) that permits integration of the vector into the host cell'sgenome or autonomous replication of the vector in the cell independentof the genome. For integration into the host cell genome, the vector mayrely on the nucleic acid sequence encoding the polypeptide or any otherelement of the vector for integration of the vector into the genome byhomologous or nonhomologous recombination.

Alternatively, the expression vector may contain additional nucleic acidsequences for directing integration by homologous recombination into thegenome of the host cell. The additional nucleic acid sequences enablethe vector to be integrated into the host cell genome at a preciselocation(s) in the chromosome(s). To increase the likelihood ofintegration at a precise location, the integrational elements shouldpreferably contain a sufficient number of nucleic acids, such as 100 to10,000 base pairs, preferably 400 to 10,000 base pairs, and mostpreferably 800 to 10,000 base pairs, which are highly homologous withthe corresponding target sequence to enhance the probability ofhomologous recombination. The integrational elements may be any sequencethat is homologous with the target sequence in the genome of the hostcell. Furthermore, the integrational elements may be non-encoding orencoding nucleic acid sequences. On the other hand, the vector may beintegrated into the genome of the host cell by non-homologousrecombination.

For autonomous replication, the vector may further comprise an origin ofreplication enabling the vector to replicate autonomously in the hostcell in question. Examples of bacterial origins of replication are P15Aori (as shown in the plasmid of FIG. 5) or the origins of replication ofplasmids pBR322, pUC19, pACYC177 (which plasmid has the P15A ori), orpACYC184 permitting replication in E. coli, and pUB110, pE194, pTA1060,or pAMβ1 permitting replication in Bacillus. Examples of origins ofreplication for use in a yeast host cell are the 2 micron origin ofreplication, ARS1, ARS4, the combination of ARS1 and CEN3, and thecombination of ARS4 and CEN6. The origin of replication may be onehaving a mutation which makes its functioning temperature-sensitive inthe host cell (see, e.g., Ehrlich, 1978, Proc Natl Acad Sci. USA75:1433).

More than one copy of a nucleic acid sequence of the present inventionmay be inserted into the host cell to increase production of the geneproduct. An increase in the copy number of the nucleic acid sequence canbe obtained by integrating at least one additional copy of the sequenceinto the host cell genome or by including an amplifiable selectablemarker gene with the nucleic acid sequence where cells containingamplified copies of the selectable marker gene, and thereby additionalcopies of the nucleic acid sequence, can be selected for by cultivatingthe cells in the presence of the appropriate selectable agent.

Many of the expression vectors for use in the present invention arecommercially available. Suitable commercial expression vectors includep3×FLAG™™ expression vectors from Sigma-Aldrich Chemicals, St. LouisMo., which includes a CMV promoter and hGH polyadenylation site forexpression in mammalian host cells and a pBR322 origin of replicationand ampicillin resistance markers for amplification in E. coli. Othersuitable expression vectors are pBluescriptII SK(−) and pBK-CMV, whichare commercially available from Stratagene, LaJolla Calif., and plasmidswhich are derived from pBR322 (Gibco BRL), pUC (Gibco BRL), pREP4, pCEP4(Invitrogen) or pPoly (Lathe et al., 1987, Gene 57:193-201).

1.4 Host Cells for Expression of Ketoreductase Polypeptides

In another aspect, the present disclosure provides a host cellcomprising a polynucleotide encoding an improved ketoreductasepolypeptide of the present disclosure, the polynucleotide beingoperatively linked to one or more control sequences for expression ofthe ketoreductase enzyme in the host cell. Host cells for use inexpressing the KRED polypeptides encoded by the expression vectors ofthe present invention are well known in the art and include but are notlimited to, bacterial cells, such as E. coli, Lactobacillus kefir,Lactobacillus brevis, Streptomyces and Salmonella typhimurium cells;fungal cells, such as yeast cells (e.g., Saccharomyces cerevisiae orPichia pastoris (ATCC Accession No. 201178)); insect cells such asDrosophila S2 and Spodoptera Sf9 cells; animal cells such as CHO, COS,BHK, 293, and Bowes melanoma cells; and plant cells. Appropriate culturemediums and growth conditions for the above-described host cells arewell known in the art.

Polynucleotides for expression of the ketoreductase may be introducedinto cells by various methods known in the art. Techniques include amongothers, electroporation, biolistic particle bombardment, liposomemediated transfection, calcium chloride transfection, and protoplastfusion. Various methods for introducing polynucleotides into cells willbe apparent to the skilled artisan.

An exemplary host cell is Escherichia coli W3110. The expression vectorwas created by operatively linking a polynucleotide encoding an improvedketoreductase into the plasmid pCK110900 operatively linked to the lacpromoter under control of the lad repressor. The expression vector alsocontained the P15a origin of replication and the chloramphenicolresistance gene. Cells containing the subject polynucleotide inEscherichia coli W3110 were isolated by subjecting the cells tochloramphenicol selection.

1.5 Methods of Generating Engineered Ketoreductase Polypeptides

In some embodiments, to make the improved KRED polynucleotides andpolypeptides of the present disclosure, the naturally-occurringketoreductase enzyme that catalyzes the reduction reaction is obtained(or derived) from Lactobacillus kefir, Lactobacillus brevis, orLactobacillus minor. In some embodiments, the parent polynucleotidesequence is codon optimized to enhance expression of the ketoreductasein a specified host cell. As an illustration, the parentalpolynucleotide sequence encoding the wild-type KRED polypeptide ofLactobacillus kefir was constructed from oligonucleotides prepared basedupon the known polypeptide sequence of Lactobacillus kefir KRED sequenceavailable in Genbank database (Genbank accession no. AAP94029GI:33112056). The parental polynucleotide sequence, designated as SEQ IDNO: 1, was codon optimized for expression in E. coli and thecodon-optimized polynucleotide cloned into an expression vector, placingthe expression of the ketoreductase gene under the control of the lacpromoter and lad repressor gene. Clones expressing the activeketoreductase in E. coli were identified and the genes sequenced toconfirm their identity. The sequence designated (SEQ ID NO: 1) was theparent sequence utilized as the starting point for most experiments andlibrary construction of engineered ketoreductases evolved from theLactobacillus kefir ketoreductase.

The engineered ketoreductases can be obtained by subjecting thepolynucleoticde encoding the naturally occurring ketoreductase tomutagenesis and/or directed evolution methods, as discussed above. Anexemplary directed evolution technique is mutagenesis and/or DNAshuffling as described in Stemmer, 1994, Proc Natl Acad Sci USA91:10747-10751; WO 95/22625; WO 97/0078; WO 97/35966; WO 98/27230; WO00/42651; WO 01/75767 and U.S. Pat. No. 6,537,746. Other directedevolution procedures that can be used include, among others, staggeredextension process (StEP), in vitro recombination (Zhao et al., 1998,Nat. Biotechnol. 16:258-261), mutagenic PCR (Caldwell et al., 1994, PCRMethods Appl. 3:S136-S140), and cassette mutagenesis (Black et al.,1996, Proc Natl Acad Sci USA 93:3525-3529).

The clones obtained following mutagenesis treatment are screened forengineered ketoreductases having a desired improved enzyme property.Measuring enzyme activity from the expression libraries can be performedusing the standard biochemistry technique of monitoring the rate ofdecrease (via a decrease in absorbance or fluorescence) of NADH or NADPHconcentration, as it is converted into NAD⁺ or NADP⁺. (For example, seeExample 7.) In this reaction, the NADH or NADPH is consumed (oxidized)by the ketoreductase as the ketoreductase reduces a ketone substrate tothe corresponding hydroxyl group. The rate of decrease of NADH or NADPHconcentration, as measured by the decrease in absorbance orfluorescence, per unit time indicates the relative (enzymatic) activityof the KRED polypeptide in a fixed amount of the lysate (or alyophilized powder made therefrom). Where the improved enzyme propertydesired is thermal stability, enzyme activity may be measured aftersubjecting the enzyme preparations to a defined temperature andmeasuring the amount of enzyme activity remaining after heat treatments.Clones containing a polynucleotide encoding a ketoreductase are thenisolated, sequenced to identify the nucleotide sequence changes (ifany), and used to express the enzyme in a host cell.

Where the sequence of the engineered polypeptide is known, thepolynucleotides encoding the enzyme can be prepared by standardsolid-phase methods, according to known synthetic methods. In someembodiments, fragments of up to about 100 bases can be individuallysynthesized, then joined (e.g., by enzymatic or chemical litigationmethods, or polymerase mediated methods) to form any desired continuoussequence. For example, polynucleotides and oligonucleotides of theinvention can be prepared by chemical synthesis using, e.g., theclassical phosphoramidite method described by Beaucage et al., 1981, TetLett 22:1859-69, or the method described by Matthes et al., 1984, EMBOJ. 3:801-05, e.g., as it is typically practiced in automated syntheticmethods. According to the phosphoramidite method, oligonucleotides aresynthesized, e.g., in an automatic DNA synthesizer, purified, annealed,ligated and cloned in appropriate vectors. In addition, essentially anynucleic acid can be obtained from any of a variety of commercialsources, such as The Midland Certified Reagent Company, Midland, Tex.,The Great American Gene Company, Ramona, Calif., ExpressGen Inc.Chicago, Ill., Operon Technologies Inc., Alameda, Calif., and manyothers.

Engineered ketoreductase enzymes expressed in a host cell can berecovered from the cells and or the culture medium using any one or moreof the well known techniques for protein purification, including, amongothers, lysozyme treatment, sonication, filtration, salting-out,ultra-centrifugation, and chromatography. Suitable solutions for lysingand the high efficiency extraction of proteins from bacteria, such as E.coli, are commercially available under the trade name CelLytic B™ fromSigma-Aldrich of St. Louis Mo.

Chromatographic techniques for isolation of the ketoreductasepolypeptide include, among others, reverse phase chromatography highperformance liquid chromatography, ion exchange chromatography, gelelectrophoresis, and affinity chromatography. Conditions for purifying aparticular enzyme will depend, in part, on factors such as net charge,hydrophobicity, hydrophilicity, molecular weight, molecular shape, etc.,and will be apparent to those having skill in the art.

In some embodiments, affinity techniques may be used to isolate theimproved ketoreductase enzymes. For affinity chromatographypurification, any antibody which specifically binds the ketoreductasepolypeptide may be used. For the production of antibodies, various hostanimals, including but not limited to rabbits, mice, rats, etc., may beimmunized by injection with an engineered polypeptide. The polypeptidemay be attached to a suitable carrier, such as BSA, by means of a sidechain functional group or linkers attached to a side chain functionalgroup. Various adjuvants may be used to increase the immunologicalresponse, depending on the host species, including but not limited toFreund's (complete and incomplete), mineral gels such as aluminumhydroxide, surface active substances such as lysolecithin, pluronicpolyols, polyanions, peptides, oil emulsions, keyhole limpet hemocyanin,dinitrophenol, and potentially useful human adjuvants such as BCG(bacilli Calmette Guerin) and Corynebacterium parvum.

1.6 Methods of Using the Engineered Ketoreductase Enzymes and CompoundsPrepared Therewith

In some embodiments, the ketoreductase enzymes described herein arecapable of catalyzing the reduction reaction of the keto group in thecompound of structural formula (I),methyl-2-benzamidomethyl-3-oxobutyrate (“the substrate”):

to the corresponding stereoisomeric alcohol product of structuralformula (II), 2S, 3R-methyl-2-benzamidomethyl-3-hydroxybutyrate (“theproduct”):

In some embodiments, the substrate of formula (I) is a racemic mixture,as shown in formula (Ia),

and the 2S,3R selective ketoreductases can be used to reduce or convertthe racemic substrate in the reaction shown in Scheme 1 below to preparethe product of formula (II):

Accordingly, in some embodiments, the ketoreductases of the disclosurecan be used in a method for stereoselectively reducing the substrate ofstructural formula (I) to the corresponding product of structuralformula (II) with at least about 60% stereomeric excess, which methodcomprises contacting or incubating the substrate of formula (I) orformula (Ia) with a 2S,3R selective ketoreductase polypeptide of thedisclosure under reaction conditions suitable for reduction orconversion of the substrate to the product of formula (II). In someembodiments of this method, the product of formula (II) is produced withat least about 85% stereomeric excess. In some embodiments of thismethod, the 2S,3R selective ketoreductase polypeptides have, withrespect to the wild-type L. kefir, L. brevis, or L. minor KRED sequencesof SEQ ID NO:4, 2, and 86, at least the following features: residue 202is valine or leucine. In some embodiments, the 2S,3R selectiveketoreductase polypeptides have, with respect to the wild-type L. kefir,L. brevis, or L. minor KRED sequences of SEQ ID NO:4, 2, and 86, atleast the following features: (1) residue corresponding to X94 is analiphatic or polar residue; (2) residue corresponding to X199 is analiphatic, constrained, or polar residue; and (3) residue correspondingto X202 is valine or leucine. In some embodiments, the 2S,3R selectiveketoreductase polypeptides have, with respect to the wild-type L. kefir,L. brevis, or L. minor KRED sequences of SEQ ID NO:4, 2, and 86, atleast the following features: (1) residue corresponding to 94 is a polarresidue, (2) residue corresponding to 199 is a constrained residue, and(3) residue corresponding to X202 is valine or leucine.

In some embodiments of the method for converting the substrate to theproduct of structural formula (II), the substrate is converted to theproduct with a percent stereomeric excess of at least about 60-89% andat a rate that is at least about 1-15 fold greater than the rate capableby the polypeptide having the amino acid sequence of SEQ ID NO:48.Exemplary polypeptides that may be used in this method include, but arenot limited to, polypeptides comprising amino acid sequencescorresponding to SEQ ID NO: 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26,28, 30, 32, 34, 36, 38, 40, 42, 46, 50, 52, 54, 56, 58, 60, and 62.

In some embodiments of the method for converting the substrate to theproduct of structural formula (II), the substrate is converted to theproduct with a percent stereomeric excess of at least about 90-94%.Exemplary polypeptides that may be used in this method include, but arenot limited to, polypeptides comprising amino acid sequencescorresponding to SEQ ID NO: 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26,28, 30, 32, 34, 36, 40, 42, 50, 52, 56, 58, 60, and 62.

In some embodiments of the method for converting the substrate to theproduct of structural formula (II), the substrate is converted to theproduct with a percent stereomeric excess of at least about 95-99%.Exemplary polypeptides that may be used in this method include, but arenot limited to, polypeptides comprising amino acid sequencescorresponding to SEQ ID NO: 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26,28, 30, 32, 34, 42, 50, 52, 56, 58, 60, and 62.

In some embodiments, the ketoreductase enzymes described herein arecapable of catalyzing the reduction reaction of the keto group in thecompound of structural formula (I) to the corresponding stereoisomericalcohol product of structural formula (III),2R,3R-methyl-2-benzamidomethyl-3-hydroxybutyrate, (which can also bereferred to as a “product”):

In some embodiments, the substrate of formula (I) is a racemic mixtureas shown in formula (Ia), and the 2R,3R selective ketoreductases can beused to reduce or convert the racemic substrate in the reaction shown inScheme 3 below to prepare the product of formula (III):

In some embodiments of the method for converting the substrate to theproduct of structural formula (III), the substrate is converted to theproduct with a percent stereomeric excess of at least about 85%.Exemplary polypeptides that may be used in this method include, but arenot limited to, polypeptides comprising amino acid sequencescorresponding to SEQ ID NO: 68, 72, 74, 76, 78, and 82.

In some embodiments of the method for converting the substrate to theproduct of structural formula (III), the substrate is converted to theproduct at a rate that is at least about 1 fold greater than the ratecapable by the polypeptide having the amino acid sequence of SEQ IDNO:66. Exemplary polypeptides that may be used in this method include,but are not limited to, polypeptides comprising amino acid sequencescorresponding to SEQ ID NO: 64, 68, 70, 72, 74, 76, 78. 80, and 82.

In some embodiments, the ketoreductases described herein can be used ina method for synthesizing a carbapenem, the method comprising thegeneral process shown below (Scheme 3),

where the KRED can be any one of the ketoreductase polypeptidesdisclosed herein. The carbapenem of the general formula (V) aredescribed in further detail below. For the synthesis of variouscarbapenem based therapeutics, an important intermediate is the compoundof structural formula (IVa),

where R¹ is H or a hydroxyl protecting group, and R¹⁰ is a halogen(e.g., Cl), or —OAc (Ac is acetate). Various hydroxyl protecting groupsare known in the art, and include, by way of example and not limitation,silyl ethers (e.g., t-butyl dimethyl silyl) and substituted benzylethers (see, Green and Wuts, Protective Groups in Organic Synthesis,Wiley-Interscience, New York, 1999). Accordingly, in a method for thesynthesis of the intermediate of structural formula (IVa), a step in themethod comprises contacting or reacting the substrate of formula (I)with the ketoreductases of the disclosure under reaction conditionssuitable for reducing or converting the substrate to the product offormula (II). The synthesis of the intermediate of formula (IVa) inwhich R¹⁰ is —OAc is described in Tetrahedron Lett. 23:2293 (1982);Tetrahedron Lett. 39:2399 (1983); Tetrahedron Lett. 39:2505 (1983);EP0290385; and EP0369691; all references incorporated herein byreference. In some embodiments, the intermediate of formula (IVa) inwhich R¹⁰ is —OAc can be synthesized as illustrated in Scheme 4:

In Scheme 4, the method comprises: (a) reducing the substrate of formula(I) to the product of formula (II) by contacting or reacting thesubstrate with a 2S,3R selective ketoreductase of the present disclosureunder reaction conditions suitable for reducing the substrate to theproduct of formula (II); (b) removing the group —C(O)C₆H₅ to formcompound (VI); (c) converting the compound of formula (VI) to the□-lactam of formula (VII) by reacting with triphenylphosphine andN-tert-butyl-2-benzothiazolylsulfenamide (see, e.g., Tetrahedron Lett.1995, 36(21):3703); (d) reacting with tert-butyl dimethyl chlorosilane(TBDMS-Cl) to form the compound of formula (VIII); and (e) acetoxylatingthe compound of formula (VIII) in presence of peracetic acid andruthenium to form the intermediate of formula (IV) (see, e.g., Murahashiet al., 1990, J. Am. Chem. Soc. 112(21):7820-7822).

In some embodiments, another intermediate in the synthesis of carbapenembased therapeutics is the intermediate of structural formula (IX):

where R² is H or a C1-C4 alkyl (e.g., —CH₃); R³ is H, or a hydroxylprotecting group; R⁴ is H, carboxy protecting group, ammonia group,alkali metal, or alkaline earth metal; and X is OH, or a leaving group.Exemplary leaving groups include, but are not limited to, —OP(O)(OR′) orOS(O2)R″, where R′ and R″ can be C1-C6 alkyl, C1-C6 alkaryl, aryl,perfluoro C1-C6 alkyl. Protecting groups for R⁴ can be, but not limitedto, benzyl, p-nitrobenzyl, and methoxymethyl. Descriptions of theintermediate of structural formula (IX) and its synthesis is provided invarious references, e.g., U.S. Pat. Nos. 5,317,016; 4,933,333; and WO0236594; the disclosures of which are incorporated herein by reference.Accordingly, in some embodiments, in a method for the synthesis of theintermediate of formula (IX), a step in the method comprises contactingor reacting the substrate of formula (I) with the ketoreductases of thedisclosure under reaction conditions suitable for reducing or convertingthe substrate to the product of formula (II).

In some embodiments, the ketoreductases of the disclosure can be used ina process for synthesis of carbapenem based therapeutic compounds ofstructural formula (V):

or solvates, hydrates, salts, and prodrugs thereof, where R² is H or—CH₃; R⁵ can be various substituents, including, but not limited to,substituted or unsubstituted alkyl, substituted or unsubstituted aryl,substituted or unsubstituted heteroalkyl, substituted or unsubstitutedheterocycloalkyl, and substituted or unsubstituted heteroarylalkyl; andR⁶ is H, or a progroup, such as a hydrolyzable ester group. As usedherein, progroup refers to a type of protecting group that, when used tomask a functional group within an active drug to form a promoiety,converts the drug into a prodrug. Progroups are typically attached tothe functional group of the drug via bonds that are cleavable underspecified conditions of use. Thus, a progroup is that portion of apromoiety that cleaves to release the functional group under thespecified conditions of use. A carboxyl group may be masked as an ester(including silyl esters and thioesters), amide or hydrazide promoiety,which may be hydrolyzed in vivo to provide the carboxyl group. Otherspecific examples of suitable progroups and their respective promoietieswill be apparent to those of skill in the art. Accordingly, in themethod for the synthesis of the compound of structural formula (V), astep in the method can comprise contacting or reacting the substrate offormula (I) with the ketoreductases of the disclosure under reactionconditions suitable for reducing or converting the substrate to theproduct of formula (II). Synthesis of various carbapenem basedtherapeutic compounds are described in, among others, U.S. Pat. Nos.4,925,836; 5,317,016; WO 02/036594; WO2004/067532; and WO 2007/104221;the disclosures of which are incorporated herein by reference.

In some embodiments, the ketoreductases of the disclosure can be usedfor the synthesis of Imipenem of the following structure (X):

or solvates, hydrates, prodrugs, and salts thereof. Imipenem has a broadspectrum of activity against aerobic and anaerobic Gram positive andGram negative bacteria. It is particularly effective against Pseudomonasaeruginosa and the Enterococcus species. Accordingly, in a method forthe synthesis of Imipenem of structural formula (X), a step in themethod comprises contacting or reacting the substrate of formula (I)with the ketoreductases of the disclosure under reaction conditionssuitable for reducing or converting the substrate to the product offormula (II). Process of preparing Imipenem from the intermediate ofstructural formula (VI) is described in WO 0236594, incorporated hereinby reference.

In some embodiments, the ketoreductases of the disclosure can be used inthe synthesis of Doripenem of structural formula (XI):

or solvates, hydrates or salts thereof. Doripenem has a spectrum andpotency against Gram-positive cocci similar to Imipenem or Ertapenem,and a Gram-negative activity similar to Meropenem. Accordingly, in amethod for the synthesis of Doripenem of structural formula (XI), a stepin the method comprises contacting or reacting the substrate of formula(I) with a ketoreductase of the present disclosure under reactionconditions suitable for reducing or converting the substrate to theproduct of formula (II). The process of preparing Doripenem from theintermediate of formula (VI) is described in U.S. Pat. No. 5,317,016,incorporated herein by reference.

In some embodiments, the ketoreductases of the disclosure can be used inthe synthesis of Meropenem of structural formula (XII):

or solvates, hydrates, prodrugs, and salts thereof. Meropenem isindicated for treatment of intra-abdominal infections, e.g.,appendicitis and peritonitis; treatment of bacterial meningitis; andtreatment of skin and skin structure infections caused by susceptibleorganisms. Accordingly, in a method for the synthesis of Meropenem offormula (XII), a step in the method comprises contacting or reacting thesubstrate of formula (I) with a ketoreductase of the present disclosureunder reaction conditions suitable for reducing or converting thesubstrate to the product of formula (II). A process for preparingMeropenem is described in WO 2007/104221, incorporated herein byreference.

In some embodiments, the ketoreductases of the disclosure can be used inthe synthesis of Ertapenem of structural formula (XIII):

or solvates, hydrates, prodrugs, and salts thereof. Ertapenem iseffective against Gram negative bacteria, but not active against MRSA,ampicillin-resistant enterococci, Pseudomonas aeruginosa orAcinetobacter species. Ertapenem also has clinically useful activityagainst anaerobic bacteria. Ertapenem is primarily used against extendedspectrum beta-lactamase (ESBL)-producing and high level AmpC-producingGram-negative bacteria. Accordingly, in a method for the synthesis ofErtapenem of formula (XIII), a step in the method comprises contactingor reacting the substrate of formula (I) with the ketoreductases of thedisclosure under reaction conditions suitable for reducing or convertingthe substrate to the product of formula (II). Processes for preparingErtapenem is described in U.S. Pat. Nos. 5,478,820 and 7,342,005,incorporated herein by reference.

In some embodiments, the ketoreductases of the disclosure can be used inthe synthesis of Biapenem of structural formula (XIV):

or solvates, hydrates, prodrugs, or salts thereof. Biapenem is aparenteral carbapenem that possesses antibacterial activities against awide range of Gram-positive and -negative bacteria, and is stable tohuman renal dehydropeptidase-I (DHP-I). It also shows in vitro activityagainst anaerobic bacteria. Accordingly, in a method for the synthesisof Biapenem of formula (XIV), a step in the method comprises contactingor reacting the substrate of formula (I) with the ketoreductases of thedisclosure under reaction conditions suitable for reducing or convertingthe substrate to the product of formula (II). Process of preparingBiapenem from intermediate (IVa) is described in U.S. Pat. No.4,925,836, incorporated herein by reference.

In some embodiments, the ketoreductases of the disclosure can be used inthe synthesis of Panipenem of structural formula (XII):

or solvates, hydrates, and salts thereof. Accordingly, in a method forthe synthesis of Panipenem of formula (XV), a step in the methodcomprises contacting or reacting the substrate of formula (I) with theketoreductases of the disclosure under reaction conditions suitable forreducing or converting the substrate to the product of formula (II).Panipenem from the intermediate of formula (II) is described in Miyaderaet al., 1983, J Antibiotic (Tokyo) 36(8):1034-1039; and Hirai et al.,1999, J. Synth Org. Chem. 57(5):382-386, incorporated herein byreference.

In some embodiments, the ketoreductases of the disclosure can be used ina method for the synthesis of sulopenem compounds of formula (XVI):

where R⁶ is H or a progroup, and R⁸ can be substituted or unsubstitutedalkyl, substituted or unsubstituted aryl; substituted or unsubstitutedheteroalkyl, substituted or unsubstituted heterocycloalkyl, andsubstituted or unsubstituted heteroarylalkyl, or —SR⁹, where R⁹ can besubstituents as described for R⁸. Other substituents for R⁸ that are inbioactive sulopenem therapeutic compounds are known in the art, some ofwhich are further described below. Descriptions of sulopenems can befound in, among others, U.S. Pat. Nos. 3,951,954; 4,234,579, 4,287,181;4,452,796; 4,343,693; 4,348,264; 4,416,891; 4,457,924; and 5,013,729;5,506,225; Volkmann et al., 1992, J. Org. Chem. 57:4352-4361; andVolkmann and O'Neill, 1991, Strategies and Tactics in Organic Synthesis,Vol 13, pg 485-534; the disclosures of which are incorporated herein byreference. Accordingly, in a method for the synthesis of a sulopenem ofstructural formula (XVI), a step in the method comprises contacting orreacting the substrate of formula (I) with the ketoreductases of thedisclosure under reaction conditions suitable for reducing or convertingthe substrate to the product of formula (II).

In some embodiments, the ketoreductases of the disclosure can be used ina method for the synthesis of a sulopenem of formula (XVII):

or solvates, hydrates, prodrugs, and salts thereof, where R⁶ is H or aprogroup. Accordingly, in a method for the synthesis of the compound offormula (XVII), a step in the method comprises contacting or reactingthe substrate of formula (I) with the ketoreductases of the disclosureunder reaction conditions suitable for reducing or converting thesubstrate to the product of formula (II). A process for the synthesis ofthe sulopenem of formula (XVII) is described in U.S. Pat. No. 5,013,729.Various progroups for R⁶ are described in US application publication2008/0009474, US application publication 2008/0125408; and Wujcik etal., 2008, Rapid Commun. Mass Spectrom. 22:3195-3206; the disclosures ofwhich are incorporated herein by reference.

In some embodiments, the ketoreductases of the disclosure can be used ina method for the synthesis of a sulopenem of structural formula (XVIII):

or solvates, hydrates, prodrugs, and salts thereof, where R⁶ is H or aprogroup. Accordingly, in a method for the synthesis of Panipenem offormula (XVIII), a step in the method comprises contacting or reactingthe substrate of formula (I) with the ketoreductases of the disclosureunder reaction conditions suitable for reducing or converting thesubstrate to the product of formula (II). Process for synthesis of thesulopenem of formula (XVIII) is described in U.S. Pat. No. 5,506,225,and WO 2007/039885.

Another sulopenem compound that can be synthesized using theketoreductases disclosed herein is the sulopenem of formula (XIX):

Accordingly, in a method for the synthesis of the compound of formula(XIX), or solvates, hydrates, prodrugs, and salts thereof, a step in themethod comprises contacting or reacting the substrate of formula (I)with the ketoreductases of the disclosure under reaction conditionssuitable for reducing or converting the substrate to the product offormula (II). Ritipenem of structural formula (XIX) is described in U.S.Pat. No. 4,482,565.

In some embodiments, the ketoreductases of the disclosure can be used ina method for the synthesis of a sulopenem of structural formula (XX):

or solvates, hydrates, prodrugs, and salts thereof. Accordingly, in amethod for the synthesis of the compound of formula (XX), a step in themethod comprises contacting or reacting the substrate of formula (I)with the ketoreductases of the disclosure under reaction conditionssuitable for reducing or converting the substrate to the product offormula (II). The compound of structural formula (XX) is described inEP1336612; incorporated herein by reference.

In some embodiments, the ketoreductases of the disclosure can be used ina method for synthesis of the compound of structural formula (XXI):

or solvates, hydrates, prodrugs, and salts thereof. Accordingly, in amethod for the synthesis of the compound of formula (XXI), a step in themethod comprises contacting or reacting the substrate of formula (I)with the ketoreductases of the disclosure under reaction conditionssuitable for reducing or converting the substrate to the product offormula (II). The compound of structural formula (XXI) is described inJP2002114788; incorporated herein by reference.

In some embodiments, the ketoreductases of the disclosure can be used ina method for the synthesis of a sulopenem of structural formula (XXII):

or solvates, hydrates, prodrugs, and salts thereof. Accordingly, in amethod for the synthesis of the compound of formula (XXII), a step inthe method comprises contacting or reacting the substrate of formula (I)with the ketoreductases of the disclosure under reaction conditionssuitable for reducing or converting the substrate to the product offormula (II). The compound of structural formula (XXII) is described inU.S. Pat. Nos. 6,924,279 and 7,034,150, the disclosures of which areincorporated herein by reference.

In some embodiments, the ketoreductases of the disclosure can be used ina method for the synthesis of a sulopenem of structural formula (XXIII):

or solvates, hydrates, prodrugs, and salts thereof. Accordingly, in amethod for the synthesis of the compound of formula (XXIII), a step inthe method comprises contacting or reacting the substrate of formula (I)with the ketoreductases of the disclosure under reaction conditionssuitable for reducing or converting the substrate to the product offormula (II). The compound of structural formula (XXIII) is described inWO 2008/047909 and U.S. Pat. No. 5,659,043, the disclosures of which areincorporated herein by reference.

In some embodiments, the ketoreductases of the disclosure can be presentas compositions, for example reaction compositions, with the substratesacted on by the ketoreductases, and/or with the products produced by theketoreductase reaction. Accordingly, in some embodiments, a compositioncan comprise a 2S,3R selective ketoreductase of the present disclosure,and a substrate of structural formula (I). In some embodiments, acomposition can comprise a 2S,3R selective ketoreductase of the presentdisclosure, and a product of structural formula (II). In someembodiments, the composition can comprise a 2S,3R ketoreductase of thedisclosure, the substrate of formula (I) and the product of formula(II).

In some embodiments, a composition can comprise a 2R,3R selectiveketoreductase of the present disclosure, and a substrate of structuralformula (I). In some embodiments, a composition can comprise a 2R,3Rselective ketoreductase of the present disclosure, and a product ofstructural formula (III). In some embodiments, the composition cancomprise a 2R,3R ketoreductase of the disclosure, the substrate offormula (I) and the product of formula (III).

Because the ketoreductase reactions can be carried out in the presenceof a co-factor (NADH or NADPH) regenerating system, the reactionconditions can further include elements of a co-factor regeneratingsystem, which are described in further detail below. Accordingly, insome embodiments, the foregoing compositions of ketoreductases canfurther include a cofactor regenerating system comprising glucosedehydrogenase and glucose; formate dehydrogenase and formate; orisopropanol and a secondary alcohol dehydrogenase. In some embodiments,the secondary alcohol dehydrogenase is an engineered ketoreductase.Other enzymes and substrates that can be used for co-factor recyclingwill be well known to the skilled artisan.

As is known by those of skill in the art, ketoreductase-catalyzedreduction reactions typically require a cofactor. Reduction reactionscatalyzed by the engineered ketoreductase enzymes described herein alsotypically require a cofactor, although many embodiments of theengineered ketoreductases require far less cofactor than reactionscatalyzed with wild-type ketoreductase enzymes. As used herein, the term“cofactor” refers to a non-protein compound that operates in combinationwith a ketoreductase enzyme. Cofactors suitable for use with theengineered ketoreductase enzymes described herein include, but are notlimited to, NADP⁺ (nicotinamide adenine dinucleotide phosphate), NADPH(the reduced form of NADP⁺), NAD⁺ (nicotinamide adenine dinucleotide)and NADH (the reduced form of NAD⁺). Generally, the reduced form of thecofactor is added to the reaction mixture. The reduced NAD(P)H form canbe optionally regenerated from the oxidized NAD(P)⁺ form using acofactor regeneration system.

The term “cofactor regeneration system” refers to a set of reactantsthat participate in a reaction that reduces the oxidized form of thecofactor (e.g., NADP⁺ to NADPH). Cofactors oxidized by theketoreductase-catalyzed reduction of the keto substrate are regeneratedin reduced form by the cofactor regeneration system. Cofactorregeneration systems comprise a stoichiometric reductant that is asource of reducing hydrogen equivalents and is capable of reducing theoxidized form of the cofactor. The cofactor regeneration system mayfurther comprise a catalyst, for example an enzyme catalyst thatcatalyzes the reduction of the oxidized form of the cofactor by thereductant. Cofactor regeneration systems to regenerate NADH or NADPHfrom NAD⁺ or NADP⁺, respectively, are known in the art and may be usedin the methods described herein.

Suitable exemplary cofactor regeneration systems that may be employedinclude, but are not limited to, glucose and glucose dehydrogenase,formate and formate dehydrogenase, glucose-6-phosphate andglucose-6-phosphate dehydrogenase, a secondary (e.g., isopropanol)alcohol and secondary alcohol dehydrogenase, phosphite and phosphitedehydrogenase, molecular hydrogen and hydrogenase, and the like. Thesesystems may be used in combination with either NADP⁺/NADPH or NAD⁺/NADHas the cofactor.

Electrochemical regeneration using hydrogenase may also be used as acofactor regeneration system. See, e.g., U.S. Pat. Nos. 5,538,867 and6,495,023, both of which are incorporated herein by reference. Chemicalcofactor regeneration systems comprising a metal catalyst and a reducingagent (for example, molecular hydrogen or formate) are also suitable.See, e.g., PCT publication WO 2000/053731, which is incorporated hereinby reference.

The terms “glucose dehydrogenase” and “GDH” are used interchangeablyherein to refer to an NAD⁺ or NADP⁺-dependent enzyme that catalyzes theconversion of D-glucose and NAD⁺ or NADP⁺ to gluconic acid and NADH orNADPH, respectively. Equation (1), below, describes the glucosedehydrogenase-catalyzed reduction of NAD⁺ or NADP⁺ by glucose.

Glucose dehydrogenases that are suitable for use in the practice of themethods described herein include both naturally occurring glucosedehydrogenases, as well as non-naturally occurring glucosedehydrogenases. Naturally occurring glucose dehydrogenase encoding geneshave been reported in the literature. For example, the Bacillus subtilis61297 GDH gene was expressed in E. coli and was reported to exhibit thesame physicochemical properties as the enzyme produced in its nativehost (Vasantha et al., 1983, Proc. Natl. Acad. Sci. USA 80:785). Thegene sequence of the B. subtilis GDH gene, which corresponds to GenbankAcc. No. M12276, was reported by Lampel et al., 1986, J. Bacteriol.166:238-243, and in corrected form by Yamane et al., 1996, Microbiology142:3047-3056 as Genbank Acc. No. D50453. Naturally occurring GDH genesalso include those that encode the GDH from B. cereus ATCC 14579(Nature, 2003, 423:87-91; Genbank Acc. No. AE017013) and B. megaterium(Eur. J. Biochem., 1988, 174:485-490, Genbank Acc. No. X12370; J.Ferment. Bioeng., 1990, 70:363-369, Genbank Acc. No. GI216270). Glucosedehydrogenases from Bacillus sp. are provided in PCT publication WO2005/018579 as SEQ ID NOS: 10 and 12 (encoded by polynucleotidesequences corresponding to SEQ ID NOS: 9 and 11, respectively, of thePCT publication), the disclosure of which is incorporated herein byreference.

Non-naturally occurring glucose dehydrogenases may be generated usingknown methods, such as, for example, mutagenesis, directed evolution,and the like. GDH enzymes having suitable activity, whether naturallyoccurring or non-naturally occurring, may be readily identified usingthe assay described in Example 4 of PCT publication WO 2005/018579, thedisclosure of which is incorporated herein by reference. Exemplarynon-naturally occurring glucose dehydrogenases are provided in PCTpublication WO 2005/018579 as SEQ ID NOS: 62, 64, 66, 68, 122, 124, and126. The polynucleotide sequences that encode them are provided in PCTpublication WO 2005/018579 as SEQ ID NOS: 61, 63, 65, 67, 121, 123, and125, respectively. All of these sequences are incorporated herein byreference. Additional non-naturally occurring glucose dehydrogenasesthat are suitable for use in the ketoreductase-catalyzed reductionreactions disclosed herein are provided in U.S. application publicationNos. 2005/0095619 and 2005/0153417, the disclosures of which areincorporated herein by reference.

Glucose dehydrogenases employed in the ketoreductase-catalyzed reductionreactions described herein may exhibit an activity of at least about 10μmol/min/mg and sometimes at least about 10² μmol/min/mg or about 10³μmol/min/mg, up to about 10⁴ μmol/min/mg or higher in the assaydescribed in Example 4 of PCT publication WO 2005/018579.

The ketoreductase-catalyzed reduction reactions described herein aregenerally carried out in a solvent. Suitable solvents include water,organic solvents (e.g., ethyl acetate, butyl acetate, 1-octanol,heptane, octane, methyl t-butyl ether (MTBE), toluene, and the like),ionic liquids (e.g., 1-ethyl 4-methylimidazolium tetrafluoroborate,1-butyl-3-methylimidazolium tetrafluoroborate,1-butyl-3-methylimidazolium hexafluorophosphate, and the like). In someembodiments, aqueous solvents, including water and aqueous co-solventsystems, are used.

Exemplary aqueous co-solvent systems have water and one or more organicsolvent. In general, an organic solvent component of an aqueousco-solvent system is selected such that it does not completelyinactivate the ketoreductase enzyme. Appropriate co-solvent systems canbe readily identified by measuring the enzymatic activity of thespecified engineered ketoreductase enzyme with a defined substrate ofinterest in the candidate solvent system, utilizing an enzyme activityassay, such as those described herein.

The organic solvent component of an aqueous co-solvent system may bemiscible with the aqueous component, providing a single liquid phase, ormay be partly miscible or immiscible with the aqueous component,providing two liquid phases. Generally, when an aqueous co-solventsystem is employed, it is selected to be biphasic, with water dispersedin an organic solvent, or vice-versa. Generally, when an aqueousco-solvent system is utilized, it is desirable to select an organicsolvent that can be readily separated from the aqueous phase. Ingeneral, the ratio of water to organic solvent in the co-solvent systemis typically in the range of from about 90:10 to about 10:90 (v/v)organic solvent to water, and between 80:20 and 20:80 (v/v) organicsolvent to water. The co-solvent system may be pre-formed prior toaddition to the reaction mixture, or it may be formed in situ in thereaction vessel.

The aqueous solvent (water or aqueous co-solvent system) may bepH-buffered or unbuffered. Generally, the reduction can be carried outat a pH of about 10 or below, usually in the range of from about 5 toabout 10. In some embodiments, the reduction is carried out at a pH ofabout 9 or below, usually in the range of from about 5 to about 9. Insome embodiments, the reduction is carried out at a pH of about 8 orbelow, often in the range of from about 5 to about 8, and usually in therange of from about 6 to about 8. The reduction may also be carried outat a pH of about 7.8 or below, or 7.5 or below. Alternatively, thereduction may be carried out a neutral pH, i.e., about 7.

During the course of the reduction reactions, the pH of the reactionmixture may change. The pH of the reaction mixture may be maintained ata desired pH or within a desired pH range by the addition of an acid ora base during the course of the reaction. Alternatively, the pH may becontrolled by using an aqueous solvent that comprises a buffer. Suitablebuffers to maintain desired pH ranges are known in the art and include,for example, phosphate buffer, triethanolamine buffer, and the like.Combinations of buffering and acid or base addition may also be used.

When the glucose/glucose dehydrogenase cofactor regeneration system isemployed, the co-production of gluconic acid (pKa=3.6), as representedin equation (3) causes the pH of the reaction mixture to drop if theresulting aqueous gluconic acid is not otherwise neutralized. The pH ofthe reaction mixture may be maintained at the desired level by standardbuffering techniques, wherein the buffer neutralizes the gluconic acidup to the buffering capacity provided, or by the addition of a baseconcurrent with the course of the conversion. Combinations of bufferingand base addition may also be used. Suitable buffers to maintain desiredpH ranges are described above. Suitable bases for neutralization ofgluconic acid are organic bases, for example amines, alkoxides and thelike, and inorganic bases, for example, hydroxide salts (e.g., NaOH),carbonate salts (e.g., NaHCO₃), bicarbonate salts (e.g., K₂CO₃), basicphosphate salts (e.g., K₂HPO₄, Na₃PO₄), and the like. The addition of abase concurrent with the course of the conversion may be done manuallywhile monitoring the reaction mixture pH or, more conveniently, by usingan automatic titrator as a pH stat. A combination of partial bufferingcapacity and base addition can also be used for process control.

When base addition is employed to neutralize gluconic acid releasedduring a ketoreductase-catalyzed reduction reaction, the progress of theconversion may be monitored by the amount of base added to maintain thepH. Typically, bases added to unbuffered or partially buffered reactionmixtures over the course of the reduction are added in aqueoussolutions.

In some embodiments, the co-factor regenerating system can comprises aformate dehydrogenase. The terms “formate dehydrogenase” and “FDH” areused interchangeably herein to refer to an NAD⁺ or NADP⁺-dependentenzyme that catalyzes the conversion of formate and NAD⁺ or NADP⁺ tocarbon dioxide and NADH or NADPH, respectively. Formate dehydrogenasesthat are suitable for use as cofactor regenerating systems in theketoreductase-catalyzed reduction reactions described herein includeboth naturally occurring formate dehydrogenases, as well asnon-naturally occurring formate dehydrogenases. Formate dehydrogenasesinclude those corresponding to SEQ ID NOS: 70 (Pseudomonas sp.) and 72(Candida boidinii) of PCT publication WO 2005/018579, which are encodedby polynucleotide sequences corresponding to SEQ ID NOS: 69 and 71,respectively, of PCT publication 2005/018579, the disclosures of whichare incorporated herein by reference. Formate dehydrogenases employed inthe methods described herein, whether naturally occurring ornon-naturally occurring, may exhibit an activity of at least about 1μmol/min/mg, sometimes at least about 10 μmol/min/mg, or at least about10² μmol/min/mg, up to about 10³ μmol/min/mg or higher, and can bereadily screened for activity in the assay described in Example 4 of PCTpublication WO 2005/018579.

As used herein, the term “formate” refers to formate anion (HCO₂),formic acid (HCO₂H), and mixtures thereof. Formate may be provided inthe form of a salt, typically an alkali or ammonium salt (for example,HCO₂Na, KHCO₂NH₄, and the like), in the form of formic acid, typicallyaqueous formic acid, or mixtures thereof. Formic acid is a moderateacid. In aqueous solutions within several pH units of its pKa (pKa=3.7in water) formate is present as both HCO₂ and HCO₂H in equilibriumconcentrations. At pH values above about pH 4, formate is predominantlypresent as HCO₂. When formate is provided as formic acid, the reactionmixture is typically buffered or made less acidic by adding a base toprovide the desired pH, typically of about pH 5 or above. Suitable basesfor neutralization of formic acid include, but are not limited to,organic bases, for example amines, alkoxides and the like, and inorganicbases, for example, hydroxide salts (e.g., NaOH), carbonate salts (e.g.,NaHCO₃), bicarbonate salts (e.g., K₂CO₃), basic phosphate salts (e.g.,K₂HPO₄, Na₃PO₄), and the like.

For pH values above about pH 5, at which formate is predominantlypresent as HCO₂, Equation (2) below, describes the formatedehydrogenase-catalyzed reduction of NAD⁺ or NADP⁺ by formate.

When formate and formate dehydrogenase are employed as the cofactorregeneration system, the pH of the reaction mixture may be maintained atthe desired level by standard buffering techniques, wherein the bufferreleases protons up to the buffering capacity provided, or by theaddition of an acid concurrent with the course of the conversion.Suitable acids to add during the course of the reaction to maintain thepH include organic acids, for example carboxylic acids, sulfonic acids,phosphonic acids, and the like, mineral acids, for example hydrohalicacids (such as hydrochloric acid), sulfuric acid, phosphoric acid, andthe like, acidic salts, for example dihydrogenphosphate salts (e.g.,KH₂PO₄), bisulfate salts (e.g., NaHSO₄) and the like. Some embodimentsutilize formic acid, whereby both the formate concentration and the pHof the solution are maintained.

When acid addition is employed to maintain the pH during a reductionreaction using the formate/formate dehydrogenase cofactor regenerationsystem, the progress of the conversion may be monitored by the amount ofacid added to maintain the pH. Typically, acids added to unbuffered orpartially buffered reaction mixtures over the course of conversion areadded in aqueous solutions.

The terms “secondary alcohol dehydrogenase” and “sADH” are usedinterchangeably herein to refer to an NAD⁺ or NADP⁺-dependent enzymethat catalyzes the conversion of a secondary alcohol and NAD⁺ or NADP⁺to a ketone and NADH or NADPH, respectively. Equation (3), below,describes the reduction of NAD⁺ or NADP⁺ by a secondary alcohol,illustrated by isopropanol.

Secondary alcohol dehydrogenases that are suitable for use as cofactorregenerating systems in the ketoreductase-catalyzed reduction reactionsdescribed herein include both naturally occurring secondary alcoholdehydrogenases, as well as non-naturally occurring secondary alcoholdehydrogenases. Naturally occurring secondary alcohol dehydrogenasesinclude known alcohol dehydrogenases from, Thermoanerobium brockii,Rhodococcus etythropolis, Lactobacillus kefir, and Lactobacillus brevis,and non-naturally occurring secondary alcohol dehydrogenases includeengineered alcohol dehydrogenases derived therefrom. Secondary alcoholdehydrogenases employed in the methods described herein, whethernaturally occurring or non-naturally occurring, may exhibit an activityof at least about 1 μmol/min/mg, sometimes at least about 10μmol/min/mg, or at least about 10² μmol/min/mg, up to about 10³μmol/min/mg or higher.

Suitable secondary alcohols include lower secondary alkanols andaryl-alkyl carbinols. Examples of lower secondary alcohols includeisopropanol, 2-butanol, 3-methyl-2-butanol, 2-pentanol, 3-pentanol,3,3-dimethyl-2-butanol, and the like. In one embodiment the secondaryalcohol is isopropanol. Suitable aryl-akyl carbinols includeunsubstituted and substituted 1-arylethanols.

When a secondary alcohol and secondary alcohol dehydrogenase areemployed as the cofactor regeneration system, the resulting NAD⁺ orNADP⁺ is reduced by the coupled oxidation of the secondary alcohol tothe ketone by the secondary alcohol dehydrogenase. Some engineeredketoreductases also have activity to dehydrogenate a secondary alcoholreductant. In some embodiments using secondary alcohol as reductant, theengineered ketoreductase and the secondary alcohol dehydrogenase are thesame enzyme.

In carrying out embodiments of the ketoreductase-catalyzed reductionreactions described herein employing a cofactor regeneration system,either the oxidized or reduced form of the cofactor may be providedinitially. As described above, the cofactor regeneration system convertsoxidized cofactor to its reduced form, which is then utilized in thereduction of the ketoreductase substrate.

In some embodiments, cofactor regeneration systems are not used. Forreduction reactions carried out without the use of a cofactorregenerating systems, the cofactor is added to the reaction mixture inreduced form.

In some embodiments, when the process is carried out using whole cellsof the host organism, the whole cell may natively provide the cofactor.Alternatively or in combination, the cell may natively or recombinantlyprovide the glucose dehydrogenase.

In carrying out the stereoselective reduction reactions describedherein, the engineered ketoreductase enzyme, and any enzymes comprisingthe optional cofactor regeneration system, may be added to the reactionmixture in the form of the purified enzymes, whole cells transformedwith gene(s) encoding the enzymes, and/or cell extracts and/or lysatesof such cells. The gene(s) encoding the engineered ketoreductase enzymeand the optional cofactor regeneration enzymes can be transformed intohost cells separately or together into the same host cell. For example,in some embodiments one set of host cells can be transformed withgene(s) encoding the engineered ketoreductase enzyme and another set canbe transformed with gene(s) encoding the cofactor regeneration enzymes.Both sets of transformed cells can be utilized together in the reactionmixture in the form of whole cells, or in the form of lysates orextracts derived therefrom. In other embodiments, a host cell can betransformed with gene(s) encoding both the engineered ketoreductaseenzyme and the cofactor regeneration enzymes.

Whole cells transformed with gene(s) encoding the engineeredketoreductase enzyme and/or the optional cofactor regeneration enzymes,or cell extracts and/or lysates thereof, may be employed in a variety ofdifferent forms, including solid (e.g., lyophilized, spray-dried, andthe like) or semisolid (e.g., a crude paste).

The cell extracts or cell lysates may be partially purified byprecipitation (ammonium sulfate, polyethyleneimine, heat treatment orthe like, followed by a desalting procedure prior to lyophilization(e.g., ultrafiltration, dialysis, and the like). Any of the cellpreparations may be stabilized by crosslinking using known crosslinkingagents, such as, for example, glutaraldehyde or immobilization to asolid phase (e.g., Eupergit C, and the like).

The solid reactants (e.g., enzyme, salts, etc.) may be provided to thereaction in a variety of different forms, including powder (e.g.,lyophilized, spray dried, and the like), solution, emulsion, suspension,and the like. The reactants can be readily lyophilized or spray driedusing methods and equipment that are known to those having ordinaryskill in the art. For example, the protein solution can be frozen at−80° C. in small aliquots, then added to a prechilled lyophilizationchamber, followed by the application of a vacuum. After the removal ofwater from the samples, the temperature is typically raised to 4° C. fortwo hours before release of the vacuum and retrieval of the lyophilizedsamples.

The quantities of reactants used in the reduction reaction willgenerally vary depending on the quantities of product desired, andconcomitantly the amount of ketoreductase substrate employed. Thefollowing guidelines can be used to determine the amounts ofketoreductase, cofactor, and optional cofactor regeneration system touse. Generally, keto substrates can be employed at a concentration ofabout 20 to 300 grams/liter using from about 50 mg to about 5 g ofketoreductase and about 10 mg to about 150 mg of cofactor. Those havingordinary skill in the art will readily understand how to vary thesequantities to tailor them to the desired level of productivity and scaleof production. Appropriate quantities of optional cofactor regenerationsystem may be readily determined by routine experimentation based on theamount of cofactor and/or ketoreductase utilized. In general, thereductant (e.g., glucose, formate, isopropanol) is utilized at levelsabove the equimolar level of ketoreductase substrate to achieveessentially complete or near complete conversion of the ketoreductasesubstrate.

The order of addition of reactants is not critical. The reactants may beadded together at the same time to a solvent (e.g., monophasic solvent,biphasic aqueous co-solvent system, and the like), or alternatively,some of the reactants may be added separately, and some together atdifferent time points. For example, the cofactor regeneration system,cofactor, ketoreductase, and ketoreductase substrate may be added firstto the solvent.

For improved mixing efficiency when an aqueous co-solvent system isused, the cofactor regeneration system, ketoreductase, and cofactor maybe added and mixed into the aqueous phase first. The organic phase maythen be added and mixed in, followed by addition of the ketoreductasesubstrate. Alternatively, the ketoreductase substrate may be premixed inthe organic phase, prior to addition to the aqueous phase

Suitable conditions for carrying out the ketoreductase-catalyzedreduction reactions described herein include a wide variety ofconditions which can be readily optimized by routine experimentationthat includes, but is not limited to, contacting the engineeredketoreductase enzyme and substrate at an experimental pH and temperatureand detecting product, for example, using the methods described in theExamples provided herein.

The ketoreductase catalyzed reduction is typically carried out at atemperature in the range of from about 15° C. to about 75° C. For someembodiments, the reaction is carried out at a temperature in the rangeof from about 20° C. to about 55° C. In still other embodiments, it iscarried out at a temperature in the range of from about 20° C. to about45° C. The reaction may also be carried out under ambient conditions.

The reduction reaction is generally allowed to proceed until essentiallycomplete, or near complete, reduction of substrate is obtained.Reduction of substrate to product can be monitored using known methodsby detecting substrate and/or product. Suitable methods include gaschromatography, HPLC, and the like. Conversion yields of the alcoholreduction product generated in the reaction mixture are generallygreater than about 50%, may also be greater than about 60%, may also begreater than about 70%, may also be greater than about 80%, may also begreater than 90%, and are often greater than about 97%.

EXAMPLES

Various features and embodiments of the disclosure are illustrated inthe following representative examples, which are intended to beillustrative, and not limiting.

Example 1: Production of Ketoreductase Powders; Shake Flask Procedure

A single microbial colony of E. coli containing a plasmid with theketoreductase gene of interest was inoculated into 50 ml Tryptic broth(12 g/L bacto-tryptone, 24 g/L yeast extract, 4 ml/L glycerol, 65 mMpotassium phosphate, pH 7.0,) containing 30 μg/ml chloramphenicol and 1%glucose in a 250 ml Erlenmeyer flask. Cells were grown overnight (atleast 16 hrs) in an incubator at 30° C. with shaking at 250 rpm. Theculture was diluted into 250 ml Terrific Broth containing 1 mM MgSO₄, 30μg/ml chloramphenicol in a 1 liter flask to an optical density at 600 nm(OD600) of 0.2 and allowed to grow at 30° C. Expression of theketoreductase gene was induced with 1 mM IPTG when the OD600 of theculture is 0.6 to 0.8 and incubated overnight (at least 16 hrs). Cellswere harvested by centrifugation (5000 rpm, 15 min, 4° C.) and thesupernatant was discarded. The cell pellet was resuspended with an equalvolume of cold (4° C.) 100 mM triethanolamine(chloride) buffer, pH 7.0(including 1 mM MgSO₄ in the case of ADH-LK and ADH-LB and engineeredketoreductases derived there from), and harvested by centrifugation asabove. The washed cells were resuspended in 12 ml of the coldtriethanolamine(chloride) buffer and passed through a French Press twiceat 12000 psi while maintained at 4° C. Cell debris was removed bycentrifugation (9000 rpm, 45 min., 4° C.). The clear lysate supernatantwas collected and stored at −20° C. Lyophilization of frozen clearlysate provided a dry powder of crude ketoreductase enzyme.

Example 2: Production of Ketoreductases; Fermentation Procedure

In an aerated agitated 15 L fermenter, 6.0 L of growth medium containing0.88 g/L ammonium sulfate, 0.98 g/L of sodium citrate; 12.5 g/L ofdipotassium hydrogen phosphate trihydrate, 6.25 g/L of potassiumdihydrogen phosphate, 6.2 g/L of Tastone-154 yeast extract, 0.083 g/Lferric ammonium citrate, and 8.3 ml/L of a trace element solutioncontaining 2 g/L of calcium chloride dihydrate, 2.2 g/L of zinc sulfateseptahydrate, 0.5 g/L manganese sulfate monohydrate, 1 g/L cuproussulfate heptahydrate, 0.1 g/L ammonium molybdate tetrahydrate and 0.02g/L sodium tetraborate decahydrate was brought to a temperature of 30°C. The fermenter was inoculated with a late exponential culture of E.coli W3110, containing a plasmid with the ketoreductase gene ofinterest, grown in a shake flask as described in Example 3 to a startingOD600 of 0.5 to 2.0. The fermenter was agitated at 500-1500 rpm and airwas supplied to the fermentation vessel at 1.0-15.0 L/min to maintaindissolved oxygen level of 30% saturation or greater. The pH of theculture was controlled at 7.0 by addition of 20% v/v ammonium hydroxide.Growth of the culture was maintained by the addition of a feed solutioncontaining 500 g/L cerelose, 12 g/L ammonium chloride and 10.4 g/Lmagnesium sulfate heptahydrate. After the culture reached an OD600 of50, the expression of ketoreductase was induced by the addition ofisopropyl-β-D-thiogalactoside (IPTG) to a final concentration of 1 mM.The culture was grown for another 14 hours. The culture was then chilledto 4° C. and maintained at 4° C. until harvested. Cells were harvestedby centrifugation at 5000 G for 40 minutes in a Sorval RC12BP centrifugeat 4° C. Harvested cells were used directly in the following downstreamrecovery process or were stored at 4° C. until such use.

The cell pellet was resuspended in 2 volumes of 100 mMtriethanolamine(chloride) buffer, pH 6.8, at 4° C. to each volume of wetcell paste. The intracellular ketoreductase was released from the cellsby passing the suspension through a homogenizer fitted with a two-stagehomogenizing valve assembly using a pressure of 12000 psig. The cellhomogenate was cooled to 4° C. immediately after disruption. A solutionof 10% w/v polyethyleneimine, pH 7.2, was added to the lysate to a finalconcentration of 0.5% w/v and stirred for 30 minutes. The resultingsuspension was clarified by centrifugation at 5000 G in a standardlaboratory centrifuge for 30 minutes. The clear supernatant was decantedand concentrated ten fold using a cellulose ultrafiltration membranewith a molecular weight cut off of 30Kd. The final concentrate wasdispensed into shallow containers, frozen at −20° C. and lyophilized topowder. The ketoreductase powder was stored at −80° C.

Example 3: Analytical Methods for the Detection ofMethyl-2-Benzamidomethyl-3-Hydroxybutyrate Stereoisomers

For routine analysis, the 2 stereoisomers ofmethyl-2-benzamidomethyl-3-oxobutyrate and the 4 stereoisomers ofmethyl-2-benzamidomethyl-3-hydroxybutyrate were separated by normalphase chiral HPLC on a Chiralpak IA column (4.6×150 mm (Chiraltechnologies, cat #80324); isocratic (92% heptane, 8% ethanol); 40° C.;1.5 mL/min flow rate; sample volume: 10 μL; detection: UV absorbance at254 nm). Retention times: 2S,3R-stereoisomer:6.8 min.,2R,3S-diastereomer: 8.1 min, 2R,3R-stereoisomer: 9.3 min,2S,3S-diastereomer: 10.1 min., substrate stereomers: 11.6 and 13.5 min.

Example 4: High Throughput NADPH Fluorescence Prescreen to IdentifyVariants Active on Isopropyl Alcohol (IPA)

Plasmid libraries obtained by directed evolution and containing evolvedketoreductase genes were transformed into E. coli and plated onLuria-Bertani (LB) broth containing 1% glucose and 30 μg/mLchloramphenicol (CAM). After incubation for at least 16 hrs at 30° C.,colonies were picked using a Q-Bot® robotic colony picker (Genetix USA,Inc., Beaverton, Oreg.) into 96-well shallow well microtiter platescontaining 180 μL Luria-Bertani (LB), 1% glucose, 30 μg/mLchloramphenicol (CAM), and 2 mM MgSO₄. Cells were grown overnight at 30°C. with shaking at 200 rpm. 20 μL of this culture was then transferredinto 96-deep well plates containing 380 μL Terrific broth (TB), 2 mMMgSO₄ and 30 μg/mL CAM. After incubation of deep-well plates at 30° C.with shaking at 250 rpm for 2.5 to 3 hours (OD₆₀₀ 0.6-0.8), recombinantgene expression by the cell cultures was induced by isopropylthiogalactoside (IPTG) to a final concentration of 1 mM. The plates werethen incubated at 30° C. with shaking at 250 rpm for 15-23 hrs.

Cells were pelleted via centrifugation, resuspended in 400 μL lysisbuffer and lysed by shaking at room temperature for at least 1 hour. Thelysis buffer contained 100 mM triethanolamine(sulphate) buffer, pH7.0-7.2, 1 mg/mL lysozyme and 200 μg/mL polymixin B sulfate and 2 mMMgSO₄. The plates are then spun in the centrifuge at 4000 RPM for 10minutes at 4° C. and the clear supernatant (cleared supernatant) is usedin the fluorescent assay.

In 96-well black microtiter plates 20 μl of lysate (10-fold dilution in100 mM triethanolamine(sulfate) buffer pH7.0) was added to 180 μl of anassay mixture consisting of 100 mM triethanolamine(sulfate) buffer, pH7.0, 1 mM MgSO₄, 1 g/L NADP, and 50% isopropylalcohol and the reactionprogress measured by following the increase in fluorescence of NADPH at445 nm after excitation at 330 nm in a Flexstation (Molecular Devices,USA).

Example 5: High Throughput HPLC Assay for Ketoreductase Activity onMethyl-2-Benzamidomethyl-3-Oxobutyrate Using Isopropylalcohol forCo-Factor Recycling

Lysates were prepared as described in Example 4. Ketoreductase activitywas measured by transferring measured quantities of the cell lysatesinto the wells of Costar deep well plates (cat #3961). To 50 μL of 3mg/ml Na-NADP in 100 mM triethanolamine(sulfate) buffer pH7.0, 150 μL of3.3 mg/ml methyl-2-benzamidomethyl-3-oxobutyrate in IPA, 100 μL clearedlysate was added. The plates were heat sealed withaluminum/polypropylene laminate heat seal tape (Velocity 11 (Menlo Park,Calif.), Cat#06643-001), and incubated at room temperature for 24 hourswith shaking. At the end of the reaction, 990 μL MTBE was added to eachwell, the plates were resealed and shaken for 20 minutes. The organicphase was separated from the aqueous phase by centrifugation (4000 rpm,5 min., 4° C.) and 200 μL the organic layer transferred to a newshallow-well, 96-well plate for analysis using the methods described inExample 3.

Example 6: High Throughput HPLC Assay for Ketoreductase Activity onMethyl-2-Benzamidomethyl-3-Oxobutyrate Using Isopropylalcohol forCo-Factor Recycling at Higher Substrate Concentration

To wells of a 96-well microtiter plate was added 10 μL of 0.6 mg/mlNa-NADP in 100 mM triethanolamine(sulfate) buffer pH 7.0, 150 μL of 100mg/ml ethyl-2-benzamidomethyl-3-oxobutyrate in IPA, 10 μL cleared lysateand 130 tit of 100 mM TEA. The plates were heat sealed and incubated atroom temperature for 24 hours with shaking. At the end of the reaction,990 μL MTBE was added to each well, the plates were heat sealed againand shaken for 20 minutes. The organic phase was separated from theaqueous phase by centrifugation (4000 rpm, 5 min., 4° C.) and 200 μL theorganic layer transferred to a new shallow-well, 96-well plate foranalysis using the methods described in Example 3.

This example describes the method that was used to identify KREDvariants improved for the stereoselective reduction ofmethyl-2-benzamidomethyl-3-oxobutyrate.

Example 7: Evaluation of ADH-LK Variants for Reduction ofMethyl-2-Benzamidomethyl-3-Oxobutyrate

Several ADH-LK variants were evaluated for the stereoselective reductionof methyl-2-benzamidomethyl-3-oxobutyrate as described in Example 5.Samples were analyzed as described in Example 3.

Table 4 lists the SEQ ID NO. corresponding to the ketoreductase, thenumber of amino acid mutations from ADH-LK, the percent conversion andthe percentage of the desired (2S,3R)-stereoisomer.

TABLE 4 Number of mutations from SEQ ID NO ADH-LK activity^(A)stereoselectivity^(B) 90 1 ++ + 92 4 ++ + 96 1 + + 98 1 ++ + A+: >30%conversion, ++: >60% conversion; ^(B)+: >95% (25,3R) isomer.

The ADH-LK variant with SEQ ID No. 90 was used for further evolution ofan efficient KRED for production of(2S,3R)-methyl-2-benzamidomethyl-3-hydroxybutyrate. Similarly, an ADH-LKvariant with SEQ ID No. 94 containing 10 mutations compared to ADH-LKwhich gave primarily the (2R,3R) stereoisomer, was used for furtherevolution of an efficient KRED for production of(2R,3R)-methyl-2-benzamidomethyl-3-hydroxybutyrate.

This example shows that variants of ADH-LK can be useful for thestereoselective reduction of methyl-2-benzamidomethyl-3-oxobutyrate. Newvariants of SEQ ID No. 90 and 94 were generated in which an internalBglI site was removed. The corresponding new sequences are SEQ ID No. 48and SEQ ID No. 66 respectively.

Example 8: Reduction of Methyl-2-Benzamidomethyl-3-Oxobutyrate to(2S,3R)-Methyl-2-Benzamidomethyl-3-Hydroxybutyrate by Further EngineeredKetoreductases Derived from ADH-LK

Improved ketoreductases derived from the ADH-LK variant with SEQ-ID No.48 were evaluated for increased activity and (2S,3R)-stereoselectivityby the method described in Example 6.

TABLE 5 Activity of ADH-LK Variants for reduction ofMethyl-2-benzamidomethyl-3-oxobutyrate to(2S,3R)-methyl-2-benzamidomethyl-3-hydroxybutyrate # Mutations from SEQID ADH LK stabi- selec- No. mutations from kefir (SEQ ID: 4)activity^(a) lity^(b) tivity^(c)  2 brevis  4 kefir 48 A202V;  1 + + 38A94T; E105G; L153A;  6 + + L199A; A202L; M206F; 16 A94T; S96F; A202V; 3 + +++ 56 L153A; L199A; A202L;  3 + +++ 58 T86I; L199N; A202L;  3 ++++ 52 L153A; A202L;  2 + +++ 54 L153A; A202V;  2 + + 32 A94T; L199A;A202V;  3 ++ ++++ 34 A94T; L153A; L199H;  4 +++ ++++ A202L; 50 L153A;L199H; A202L;  3 ++ +++ 20 A94T; L199N; A202V;  3 +++ ++++ 46 L153S;A202L;  2 + + 36 A94T; L153A; L199A;  4 + ++ A202V; 26 A94T; A202L;  2+++ +++ 28 A94T; A202V;  2 ++ +++ 30 A94T; L199A; A202L;  3 +++ ++++ 22A94T; L199H; A202L;  3 ++++ ++++ 24 A94T; L199H; A202V;  3 +++ ++++ 42L153A; L199N; A202L;  3 + +++ 40 A94T; S96F; M129T;  5 + ++ A202V;M206F; 18 A80T; L153A; A202V;  3 + +++ 44 F147M; A202V;  2 + + 10 H40R;A94T; F147L;  5 +++++ + ++++ L199H; A202L; 12 H40R; A94T; L199H;  4+++++ ++++ A202L;  6 A94T; F147L; L199H;  4 +++++ + ++++ A202L;  8 A94T;L199H; A202L;  3 +++++ ++++ 60 I11F; H40R; A94F; 11 ++++ ++++ S96V;F147M; L195V; V196L; L199W; I226V; G248K; Y249W; 62 T2A; R4C; H40R; 11+++ ++++ A94G; S96V; F147M; V196L; L199W; I226V; G248K; Y249W; 14 H40R;A94F; S96V;  9 ++++ ++++ F147M; L195V; V196L; L199W; I226V; Y249W;^(a)+: 1-15-fold more active than KRED with SEQ ID No. 48; ++:15-30-fold more active than KRED with SEQ ID No. 48; +++: 30-40-foldmore active than KRED with SEQ ID No. 48; ++++: 40-50-fold more activethan KRED with SEQ ID No. 48; +++++: >50-fold more active than KRED withSEQ ID No. 48, ^(b)+: retains activity after 21 hours preincubation at40° C., ^(c)+: 60-89% (25,3R)-product; ++: 90-94% (25,3R)-product; +++:95-99% (25,3R)-product; ++++: >99% (25,3R)-product.

Example 9: Reduction of Methyl-2-Benzamidomethyl-3-Oxobutyrate to (2R,3R)-Methyl-2-Benzamidomethyl-3-Hydroxybutyrate by EngineeredKetoreductases Derived from ADH-LK

Improved ketoreductases derived from the ADH-LK variant with SEQ-ID No.66 were evaluated for increased activity and (2R,3R)-stereoselectivityby the method described in Example 6.

TABLE 6 Activity of ADH-LK Variants for reduction ofMethyl-2-benzamidomethyl-3-oxobutyrate to(2R,3R)-methyl-2-benzamidomethyl-3-hydroxybutyrate Number of Sequence -coding mutations acti- selec- SEQ ID NO mutations from kefir vity^(a)tivity^(b) 66 H40R; A94G; S96V; E145F; 10 + + F147M; Y190P; V196L;L199W; I225V; Y249W 74 I11F; H40R; A94E; 596V; 12 ++ ++ E145F; F147M;Y190P; L195V; V196L; L199W; I226V; Y249H; 82 D3V; A10T; H40R; 12 + ++A94G; 596V; F147M; Y190P; V196L; L199W; I226V; G248K; Y249H; 68 H40R;A94F; 596V; 12 ++ ++ E145F; F147M; Y190P; L195V; V196L; L199W; I226V;G248R; Y249W; 76 I11L; H40R; A94E; 10 +++ ++ 596V; F147M; Y190H; V196L;I226V; G248K; Y249H; 72 H40R; T54A; A94F; 11 +++ ++ 596V; E105K; E145D;F147M; V196L; L199W; I226V; Y249W; 78 I11F; H40R; A94G; 14 +++ ++ 596V;E145F; F147M; Y190H; L195V; V196L; L199W; A202V; I226V; Y249H; A251T; 70H40R; E78D; A94E; 11 +++ + 596V; F147M; Y190H; L195V; V196L; I226V;Y249H; T250Y; 80 K8N; V9G; I11F; 13 +++ + H40R; A94G; 596V; E145F;F147M; Y190P; V196L; I226V; G248K; Y249R; 64 V12I; H40R; A94E; 12 +++ +596V; F147M; Y190P; L195V; V196L; L199W; I226V; G248R; Y249W; ^(a)+:1-fold more active than KRED with SEQ ID NO. 66; ++: 1-2-fold moreactive than KRED with SEQ ID NO. 66; +++: >2-fold more active than KREDwith SEQ ID NO. 66; ^(b)+: <85% (2R,3R)-product; ++: >85%(2R,3R)-product.

Example 10: Preparative Scale Production of (2S,3R)-Methyl-2-Benzamidomethyl-3-Hydroxybutyrate

A 250 ml 3-neck flask with overhead stirrer was charged with methyl2-benzamidomethyl-3-ketobutyrate (25 g), isopropylalcohol (37.5 ml) and0.1 M triethanolamine(chloride)/0.04 M MgSO₄ buffer pH7.2 (30 ml). Thereaction mixture is stirred and temperature brought up to 37° C. usingan oil bath. The reaction is started with the addition of 0.5 ml 19 g/LNADP-Na followed by 2.5 ml 30 g/L KRED of SEQ ID No. 10; both assolutions in 0.1 M triethanolamine (chloride)/0.04 M MgSO₄ buffer pH7.2. The reaction progress was followed by taking 5 μl aliquots over thecourse of the reaction that were diluted with 1 ml acetonitrile,filtered through a 0.25 μm syringe filter and analyzed as described inExample 3. When the conversion exceeded 96% saturated aqueous sodiumchloride (12.5 ml) was added to the reaction mixture, followed by 40 mlethyl acetate. The reaction mixture was stirred for another 15 minutes,then filtered through a Celite pad (5 g in a fritted glass filter) undervacuum. The filter cake was washed with 20 ml ethyl acetate and the twophases of the filtrate allowed to separate. The organic layer is washedthree times with 20 ml water and concentrated on a rotary evaporator toan oil of constant weight. After removal of ethyl acetate, toluene (10ml) was added and distilled under vacuum. (2S,3R)-methyl-2-benzamidomethyl-3-hydroxybutyrate (26.47 g) was obtained asan oil containing ˜10% toluene as determined by ¹H-NMR—CDCl₃.

All publications, patents, patent applications and other documents citedin this application are hereby incorporated by reference in theirentireties for all purposes to the same extent as if each individualpublication, patent, patent application or other document wereindividually indicated to be incorporated by reference for all purposes.

What is claimed is:
 1. An engineered ketoreductase polypeptide havingketoreductase activity, wherein said ketoreductase polypeptide is atleast 85% identical to SEQ ID NO:4, and wherein the ketoreductasepolypeptide comprises a residue difference at position 153, as comparedto the amino acid sequence of SEQ ID NO:
 4. 2. The engineeredketoreductase polypeptide of claim 1, wherein said ketoreductasepolypeptide comprises at least one of the following features: theresidue at the position corresponding to position 94 is threonine; theresidue at the position corresponding to position 199 is a histidine,alanine, or asparagine, and the residue at the position corresponding toposition 202 is valine or leucine; with the proviso that theketoreductase polypeptide has an amino acid sequence in which theresidue at the position corresponding to position 94 is an aliphatic orpolar residue; the residue at the position corresponding to position 199is an aliphatic, constrained or polar residue; and the residue at theposition corresponding to position 202 is valine or leucine.
 3. Theengineered ketoreductase polypeptide of claim 1, wherein the residue atthe position corresponding to position 94 is threonine.
 4. Theengineered ketoreductase polypeptide of claim 1, wherein the residue atthe position corresponding to position 199 is alanine, histidine, orasparagine.
 5. The engineered ketoreductase polypeptide of claim 1,wherein the residue at the position corresponding to position 94 is apolar residue; the residue at the position corresponding to position 199is an aliphatic, constrained or polar residue; and the residue at theposition corresponding to position 202 is valine or leucine.
 6. Theengineered ketoreductase polypeptide of claim 1, wherein the residue atthe position corresponding to position 94 is threonine, the residue atthe position corresponding to position 199 is alanine, histidine, orasparagine; and the residue at the position corresponding to position202 is valine or leucine.
 7. The engineered ketoreductase polypeptide ofclaim 1, further comprising one or more of the following features: theresidue at the position corresponding to position 2 is a polar,non-polar, or aliphatic residue; the residue at the positioncorresponding to position 4 is a basic residue or cysteine; the residueat the position corresponding to position 11 is a non-polar, aliphatic,or aromatic residue; the residue at the position corresponding toposition 80 is a non-polar, aliphatic, or polar residue; the residue atthe position corresponding to position 86 is a non-polar, aliphatic, orpolar residue; the residue at the position corresponding to position 96is a polar, aromatic, non-polar, or aliphatic residue; the residue atthe position corresponding to position 105 is a non-polar, aliphatic,basic or acidic residue; the residue at the position corresponding toposition 129 is a non-polar or polar residue; the residue at theposition corresponding to position 147 is an aromatic, non-polar oraliphatic residue; the residue at the position corresponding to position153 is a polar, non-polar or aliphatic residue; the residue at theposition corresponding to position 190 is an aromatic or constrainedresidue; the residue at the position corresponding to position 195 is anon-polar or aliphatic residue; the residue at the positioncorresponding to position 196 is a non-polar or aliphatic residue; theresidue at the position corresponding to position 206 is a non-polar oraromatic residue; the residue at the position corresponding to position248 is a non-polar or basic residue; and the residue at the positioncorresponding to position 249 is an aromatic residue; and whereinoptionally the amino acid sequence has one or more residue differencesat other amino acid residue positions as compared to SEQ ID NO:4.
 8. Theengineered ketoreductase polypeptide of claim 1, further comprising oneor more of the following features: the residue at the positioncorresponding to position 2 is alanine; the residue at the positioncorresponding to position 4 is cysteine; the residue at the positioncorresponding to position 11 is phenylalanine; the residue at theposition corresponding to position 80 is threonine; the residue at theposition corresponding to position 86 is isoleucine; the residue at theposition corresponding to position 96 is valine or phenylalanine; theresidue at the position corresponding to position 105 is glycine; theresidue at the position corresponding to position 129 is threonine; theresidue at the position corresponding to position 147 is methionine orleucine; the residue at the position corresponding to position 153 isalanine or serine; the residue at the position corresponding to position190 is histidine or proline; the residue at the position correspondingto position 195 is valine; the residue at the position corresponding toposition 196 is leucine; the residue at the position corresponding toposition 206 is phenylalanine; the residue at the position correspondingto position 248 is lysine, or arginine; and the residue at the positioncorresponding to position 249 is tryptophan; wherein optionally theamino acid sequence has one or more residue differences at other aminoacid residue positions as compared to SEQ ID NO:4.
 9. The engineeredketoreductase polypeptide of claim 1, further comprising the featurethat the residue corresponding to X147 is an aromatic, non-polar oraliphatic residue.
 10. The engineered ketoreductase polypeptide of claim1, further comprising one or more of the following features: the residueat the position corresponding to position 96 is a polar, aromatic,non-polar, or aliphatic; the residue at the position corresponding toposition 195 is a non-polar or aliphatic residue; the residue at theposition corresponding to position 196 is a non-polar or aliphaticresidue; the residue at the position corresponding to position 248 is anon-polar or basic residue; and the residue at the positioncorresponding to position 249 is an aromatic residue.
 11. The engineeredketoreductase polypeptide of claim 1, further comprising one or more ofthe following features: the residue at the position corresponding toposition 2 is a polar, non-polar, or aliphatic residue; the residue atthe position corresponding to position 4 is a basic residue or cysteine;the residue at the position corresponding to position 11 is a non-polar,aliphatic, or aromatic residue; the residue at the positioncorresponding to position 80 is a non-polar, aliphatic, or polarresidue; the residue at the position corresponding to position 86 is anon-polar, aliphatic, or polar residue; the residue at the positioncorresponding to position 105 is a non-polar, aliphatic, basic or acidicresidue; the residue at the position corresponding to position 129 is anon-polar or polar residue; the residue at the position corresponding toposition 153 is a polar, non-polar or aliphatic residue; the residue atthe position corresponding to position 190 is an aromatic or constrainedresidue; and the residue at the position corresponding to position 206is a non-polar or aromatic residue.
 12. The engineered ketoreductasepolypeptide of claim 1, further comprising one or more of the followingfeatures: the residue at the position corresponding to position 147 isan aromatic, non-polar or aliphatic residue; and wherein optionally theamino acid sequence has one or more residue differences at other aminoacid residue positions as compared to SEQ ID NO:4.
 13. The engineeredketoreductase polypeptide of claim 1, further comprising one or more ofthe following features: the residue at the position corresponding toposition 96 is a polar, aromatic, non-polar, or aliphatic residue; theresidue at the position corresponding to position 147 is an aromatic,non-polar or aliphatic residue; and wherein optionally the amino acidsequence has one or more residue differences at other amino acid residuepositions as compared to SEQ ID NO:4.
 14. The engineered ketoreductasepolypeptide of claim 1, further comprising one or more of the followingfeatures: residue at the position corresponding to position 96 is apolar, aromatic, non-polar, or aliphatic residue; residue at theposition corresponding to position 147 is an aromatic, non-polar oraliphatic; residue at the position corresponding to position 195 is anon-polar or aliphatic residue; residue at the position corresponding toposition 196 is a non-polar or aliphatic residue; and wherein optionallythe amino acid sequence has one or more residue differences at otheramino acid residue positions as compared to SEQ ID NO:4.
 15. Theengineered ketoreductase polypeptide of claim 1, further comprising thefeature that the residue at the position corresponding to position 147is methionine or leucine.